| Description | protein subcellular localization evidence scores by manual literature curation |
| Measurement | association by literature curation |
| Association | protein-cellular component associations by integrating evidence from manual literature curation |
| Category | structural or functional annotations |
| Resource | COMPARTMENTS |
| Citation(s) | |
| Last Updated | 2015 Feb 02 |
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Attribute Similarity
Gene Attribute
Gene Similarity
1463 sets of proteins localized to cellular components from the COMPARTMENTS Curated Protein Localization Evidence Scores dataset.
| Gene Set | Description |
|---|---|
| 4-aminobutyrate transaminase complex | A homodimeric protein complex that possesses 4-aminobutyrate transaminase activity. |
| 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase complex | A homodimeric, bifunctional enzyme complex which catalyzes the synthesis and degradation of fructose 2,6-bisphosphate, and is required for both glycolysis and gluconeogenesis. |
| 6-phosphofructokinase complex | A protein complex that possesses 6-phosphofructokinase activity; homodimeric, homooctameric, and allosteric homotetrameric forms are known. |
| 90s preribosome | A large ribonucleoprotein complex considered to be the earliest preribosomal complex. In S. cerevisiae, it has a size of 90S and consists of the 35S pre-rRNA, early-associating ribosomal proteins most of which are part of the small ribosomal subunit, the U3 snoRNA and associated proteins. |
| a band | The dark-staining region of a sarcomere, in which myosin thick filaments are present; the center is traversed by the paler H zone, which in turn contains the M line. |
| acetylcholine-gated channel complex | A homo- or hetero-pentameric protein complex that forms a transmembrane channel through which ions may pass in response to acetylcholine binding. |
| acetyltransferase complex | A protein complex which is capable of acetyltransferase activity. |
| acf complex | An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2H in mammals, Isw2 in S. cerevisiae), an ACF1 homolog, and generally no other subunits, though Xenopus is an exception with a third non-conserved subunit. ACF plays roles in regulation of RNA polymerase II transcription and in DNA replication and repair. |
| acrosomal matrix | A structural framework, or 'dense core' at the interior of an acrosome. May regulate the distribution of hydrolases within the acrosome and their release during the acrosome reaction. |
| acrosomal membrane | The membrane that surrounds the acrosomal lumen. The acrosome is a special type of lysosome in the head of a spermatozoon that contains acid hydrolases and is concerned with the breakdown of the outer membrane of the ovum during fertilization. |
| acrosomal vesicle | A structure in the head of a spermatozoon that contains acid hydrolases, and is concerned with the breakdown of the outer membrane of the ovum during fertilization. It lies just beneath the plasma membrane and is derived from the lysosome. |
| actin cap | Polarized accumulation of cytoskeletal proteins (including F-actin) and regulatory proteins in a cell. An example of this is the actin cap found in Saccharomyces cerevisiae. |
| actin cytoskeleton | The part of the cytoskeleton (the internal framework of a cell) composed of actin and associated proteins. Includes actin cytoskeleton-associated complexes. |
| actin filament | A filamentous structure formed of a two-stranded helical polymer of the protein actin and associated proteins. Actin filaments are a major component of the contractile apparatus of skeletal muscle and the microfilaments of the cytoskeleton of eukaryotic cells. The filaments, comprising polymerized globular actin molecules, appear as flexible structures with a diameter of 5-9 nm. They are organized into a variety of linear bundles, two-dimensional networks, and three dimensional gels. In the cytoskeleton they are most highly concentrated in the cortex of the cell just beneath the plasma membrane. |
| actin filament bundle | An assembly of actin filaments that are on the same axis but may be oriented with the same or opposite polarities and may be packed with different levels of tightness. |
| activin a complex | A nonsteroidal regulator, composed of two covalently linked inhibin beta-A subunits (sometimes known as activin beta-A or activin/inhibin beta-A). |
| activin complex | A nonsteroidal regulator, composed of two covalently linked inhibin beta subunits, inhibin beta-A and inhibin beta-B (sometimes known as activin beta or activin/inhibin beta). There are three forms of activin complex, activin A, which is composed of 2 inhibin beta-A subunits, activin B, which is composed of 2 inhibin beta-B subunits, and activin AB, which is composed of an inhibin beta-A and an inhibin beta-B subunit. |
| activin receptor complex | A protein complex that acts as an activin receptor. Heterodimeric activin receptors, comprising one Type I activin receptor and one Type II receptor polypeptide, and heterotrimeric receptors have been observed. |
| activin responsive factor complex | A transcriptionally active complex that binds to an activin response element (ARE) in the promoter of target genes, and is composed of two SMAD2 proteins, one SMAD4 protein and a Forkhead activin signal transducer (FAST) transcription factor. |
| actomyosin | Any complex of actin, myosin, and accessory proteins. |
| actomyosin contractile ring | A cytoskeletal structure composed of actin filaments and myosin that forms beneath the plasma membrane of many cells, including animal cells and yeast cells, in a plane perpendicular to the axis of the spindle, i.e. the cell division plane. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two daughter cells. In animal cells, the contractile ring is located inside the plasma membrane at the location of the cleavage furrow. In budding fungal cells, e.g. mitotic S. cerevisiae cells, the contractile ring forms beneath the plasma membrane at the mother-bud neck before mitosis. |
| actomyosin, actin portion | The actin part of any complex of actin, myosin, and accessory proteins. |
| ada2/gcn5/ada3 transcription activator complex | A multiprotein complex that possesses histone acetyltransferase and is involved in regulation of transcription. Contains either GCN5 or PCAF in a mutually exclusive manner. The budding yeast complex includes Gcn5p, two proteins of the Ada family, and two TBP-associate proteins (TAFs); analogous complexes in other species have analogous compositions, and usually contain homologs of the yeast proteins. Both ATAC- or SAGA (see GO:0000124, SAGA complex) are involved in the acetylation of histone H3K9 and K14 residues. |
| adherens junction | A cell junction at which anchoring proteins (cadherins or integrins) extend through the plasma membrane and are attached to actin filaments. |
| aggresome | An inclusion body formed by dynein-dependent retrograde transport of an aggregated protein on microtubules. |
| aim2 inflammasome complex | A protein complex that consists of AIM2, ASC, and caspase-1. AIM2 is a member of the HN-200 protein family that appears to be the sensor of cytosolic double-stranded DNA. |
| alpha dna polymerase:primase complex | A complex of four polypeptides, comprising large and small DNA polymerase alpha subunits and two primase subunits, which catalyzes the synthesis of an RNA primer on the lagging strand of replicating DNA; the smaller of the two primase subunits alone can catalyze oligoribonucleotide synthesis. |
| alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid selective glutamate receptor complex | An assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. The AMPA receptors mediate fast synaptic transmission in the CNS and are composed of subunits GluR1-4, products from separate genes. These subunits have an extracellular N-terminus and an intracellular C-terminus. |
| alpha-beta t cell receptor complex | A T cell receptor complex in which the TCR heterodimer comprises alpha and beta chains, associated with the CD3 complex; recognizes a complex consisting of an antigen-derived peptide bound to a class I or class II MHC protein. |
| alpha9-beta1 integrin-adam8 complex | A protein complex that consists of an alpha9-beta1 integrin complex bound to the transmembrane metallopeptidase ADAM8. |
| alpha9-beta1 integrin-vascular cell adhesion molecule-1 complex | A protein complex that consists of an alpha9-beta1 integrin complex bound to vascular cell adhesion molecule-1. |
| alphav-beta3 integrin-igf-1-igf1r complex | A protein complex that consists of an alphav-beta3 integrin complex bound to insulin-like growth factor-1 (IGF-1) and type I insulin-like growth factor receptor (IGF1R). IGF1R is a heterotetramer that consists of two alpha-subunits and two beta-subunits. |
| alphav-beta3 integrin-vitronectin complex | A protein complex that consists of an alphav-beta3 integrin complex bound to vitronectin. |
| alveolar lamellar body | A specialized secretory organelle found in type II pneumocytes and involved in the synthesis, secretion, and reutilization of pulmonary surfactant. |
| alveolar lamellar body membrane | The lipid bilayer surrounding an alveolar lamellar body, a specialized secretory organelle found in type II pneumocytes and involved in the synthesis, secretion, and reutilization of pulmonary surfactant. |
| aminoacyl-trna synthetase multienzyme complex | A multienzyme complex found in all multicellular eukaryotes composed of eight proteins with aminoacyl-tRNA synthetase activities (abbreviated as: ArgRS, AspRS, GluProRS, GlnRS, IleRS, LeuRS, LysRS, MetRS where RS is the enzyme, preceded by the amino acid it uses as a substrate) as well as three non-synthetase proteins (p43, p38, and p18) with diverse functions. Several of these subunits are known dimers, so the total polypeptide count in the multisynthetase complex is at least fifteen. All of the enzymes in this assembly catalyze the same reaction, the covalent attachment of an amino acid to either the 2'- or 3'-hydroxyl of the 3'-terminal adenosine of tRNA, but using different substrates. |
| amp-activated protein kinase complex | A protein complex that possesses AMP-dependent protein kinase activity. |
| anaphase-promoting complex | A ubiquitin ligase complex that degrades mitotic cyclins and anaphase inhibitory protein, thereby triggering sister chromatid separation and exit from mitosis. Substrate recognition by APC occurs through degradation signals, the most common of which is termed the Dbox degradation motif, originally discovered in cyclin B. |
| anchored component of external side of plasma membrane | The component of the plasma membrane consisting of the gene products that are tethered to the external side of the membrane only by a covalently attached anchor, such as a lipid group embedded in the membrane. Gene products with peptide sequences that are embedded in the membrane are excluded from this grouping. |
| anchored component of membrane | The component of a membrane consisting of the gene products that are tethered to the membrane only by a covalently attached anchor, such as a lipid group that is embedded in the membrane. Gene products with peptide sequences that are embedded in the membrane are excluded from this grouping. |
| anchored component of plasma membrane | The component of the plasma membrane consisting of the gene products that are tethered to the membrane only by a covalently attached anchor, such as a lipid group, that is embedded in the membrane. Gene products with peptide sequences that are embedded in the membrane are excluded from this grouping. |
| anchoring collagen complex | Any collagen complex which links one collagen assembly, such as a collagen fibril or sheet, to other structures. |
| anchoring junction | A cell junction that mechanically attaches a cell (and its cytoskeleton) to neighboring cells or to the extracellular matrix. |
| angiogenin-pri complex | A stable heterodimer of angiogenin and placental ribonuclease inhibitor; interaction between angiogenin and PRI prevents angiogenin binding to its receptor to stimulate angiogenesis. |
| annulate lamellae | Stacks of endoplasmic reticulum (ER) membranes containing a high density of nuclear pores, thought to form from excess nuclear membrane components, that have been described in a number of different cells. Annulate lamellar membranes are continuous with and embedded within the ER. |
| ap-1 adaptor complex | A heterotetrameric AP-type membrane coat adaptor complex that consists of beta1, gamma, mu1 and sigma1 subunits and links clathrin to the membrane surface of a vesicle; vesicles with AP-1-containing coats are normally found primarily in the trans-Golgi network. In at least humans, the AP-1 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different genes (gamma1 and gamma2, mu1A and mu1B, and sigma1A, sigma1B and sigma1C). |
| ap-2 adaptor complex | A heterotetrameric AP-type membrane coat adaptor complex that consists of alpha, beta2, mu2 and sigma2 subunits, and links clathrin to the membrane surface of a vesicle; vesicles with AP-2-containing coats are normally found primarily near the plasma membrane, on endocytic vesicles. In at least humans, the AP-2 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different alpha genes (alphaA and alphaC). |
| ap-3 adaptor complex | A heterotetrameric AP-type membrane coat adaptor complex that consists of beta3, delta, mu3 and sigma3 subunits and is found associated with endosomal membranes. AP-3 does not appear to associate with clathrin in all organisms. In at least humans, the AP-3 complex can be heterogeneric due to the existence of multiple subunit isoforms encoded by different genes (beta3A and beta3B, mu3A and mu3B, and sigma3A and sigma3B). |
| ap-5 adaptor complex | An AP-type membrane coat adaptor complex that in humans consists of beta5, zeta, mu5 and sigma5 subunits and is found associated with membranes in the endosomes; it is not clear whether AP-5 forms clathrin coats in vivo. |
| ap-type membrane coat adaptor complex | Any of several heterotetrameric complexes that link clathrin (or another coat-forming molecule, as hypothesized for AP-3 and AP-4) to a membrane surface; they are found on coated pits and coated vesicles, and mediate sorting of cargo proteins into vesicles. Each AP complex contains two large (a beta and one of either an alpha, gamma, delta, or epsilon) subunits (110-130 kDa), a medium (mu) subunit (approximately 50 kDa), and a small (sigma) subunit (15-20 kDa). |
| apical cortex | The region that lies just beneath the plasma membrane on the apical edge of a cell. |
| apical dendrite | A dendrite that emerges near the apical pole of a neuron. In bipolar neurons, apical dendrites are located on the opposite side of the soma from the axon. |
| apical junction complex | A functional unit located near the cell apex at the points of contact between epithelial cells, which in vertebrates is composed of the tight junction, the zonula adherens, and desmosomes and in some invertebrates, such as Drosophila, is composed of the subapical complex (SAC), the zonula adherens and the septate junction. Functions in the regulation of cell polarity, tissue integrity and intercellular adhesion and permeability. |
| apical part of cell | The region of a polarized cell that forms a tip or is distal to a base. For example, in a polarized epithelial cell, the apical region has an exposed surface and lies opposite to the basal lamina that separates the epithelium from other tissue. |
| apical plasma membrane | The region of the plasma membrane located at the apical end of the cell. |
| apicolateral plasma membrane | The apical end of the lateral plasma membrane of epithelial cells. |
| apolipoprotein b mrna editing enzyme complex | Protein complex that mediates editing of the mRNA encoding apolipoprotein B; catalyzes the deamination of C to U (residue 6666 in the human mRNA). Contains a catalytic subunit, APOBEC-1, and other proteins (e.g. human ASP; rat ASP and KSRP). |
| apoptosome | A multisubunit protein complex involved in the signaling phase of the apoptotic process. In mammals it is typically composed of seven Apaf-1 subunits bound to cytochrome c and caspase-9. A similar complex to promote apoptosis is formed from homologous gene products in other eukaryotic organisms. |
| arp2/3 protein complex | A stable protein complex that contains two actin-related proteins, Arp2 and Arp3, and five novel proteins (ARPC1-5), and functions in the nucleation of branched actin filaments. |
| aryl hydrocarbon receptor complex | A protein complex that acts as an aryl hydrocarbon (Ah) receptor. Cytosolic and nuclear Ah receptor complexes have different subunit composition, but both contain the ligand-binding subunit AhR. |
| aster | An array of microtubules emanating from a spindle pole MTOC that do not connect to kinetochores. |
| astral microtubule | Any of the spindle microtubules that radiate in all directions from the spindle poles and are thought to contribute to the forces that separate the poles and position them in relation to the rest of the cell. |
| astrocyte end-foot | Terminal process of astrocyte abutting non-neuronal surfaces in the brain. |
| astrocyte projection | A prolongation or process extending from the soma of an astrocyte and wrapping around neurons. |
| asymmetric synapse | A type of synapse occurring between an axon and a dendritic spine or dendritic shaft. Asymmetric synapses, the most abundant synapse type in the central nervous system, involve axons that contain predominantly spherical vesicles and contain a thickened postsynaptic density. |
| atg1/ukl1 signaling complex | A protein complex consisting of ATG1/UKL1 and ATG13 along with other proteins that regulate its function (e.g. ATG17 in yeast). This complex has serine/threonine protein kinase activity and is involved in autophagosome formation. |
| atg12-atg5-atg16 complex | A protein complex required for the expansion of the autophagosomal membrane. In budding yeast, this complex consists of Atg12p, Atg5p and Atg16p. |
| atp-binding cassette (abc) transporter complex | A complex for the transport of metabolites into and out of the cell, typically comprised of four domains; two membrane-associated domains and two ATP-binding domains at the intracellular face of the membrane, that form a central pore through the plasma membrane. Each of the four core domains may be encoded as a separate polypeptide or the domains can be fused in any one of a number of ways into multidomain polypeptides. In Bacteria and Archaebacteria, ABC transporters also include substrate binding proteins to bind substrate external to the cytoplasm and deliver it to the transporter. |
| atp-sensitive potassium channel complex | A protein complex that comprises four pore-forming (Kir6.x) and four regulatory sulphonylurea receptor (SURx) subunits and forms a transmembrane channel through which ions may pass. The opening and closing of the channel is regulated by ATP: binding of ATP to the Kir6.2 subunit inhibits channel activity, whereas binding of Mg2+-complexed ATP or ADP to the SUR1 subunit stimulates channel activity. |
| atpase dependent transmembrane transport complex | A transmembrane protein complex that functions in ATPase dependent active transport across a membrane. |
| autophagic vacuole | A double-membrane-bounded compartment in which endogenous cellular material is sequestered; known as autophagosome in yeast. |
| autophagic vacuole lumen | The volume enclosed within the autophagic vacuole membrane. |
| autophagic vacuole membrane | The lipid bilayer surrounding an autophagic vacuole, a double-membrane-bounded vesicle in which endogenous cellular material is sequestered. |
| autosome | Any chromosome other than a sex chromosome. |
| axolemma | The portion of the plasma membrane surrounding an axon; it is a specialized trilaminar random mosaic of protein molecules floating within a fluid matrix of highly mobile phospholipid molecules, 7-8 nm in thickness. |
| axon | The long process of a neuron that conducts nerve impulses, usually away from the cell body to the terminals and varicosities, which are sites of storage and release of neurotransmitter. |
| axon hillock | Portion of the neuronal cell soma from which the axon originates. |
| axon initial segment | Portion of the axon proximal to the neuronal cell body, at the level of the axon hillock. The action potentials that propagate along the axon are generated at the level of this initial segment. |
| axon part | A part of an axon, a cell projection of a neuron. |
| axon terminus | Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal button is a specialized region of it. |
| axonal growth cone | The migrating motile tip of a growing nerve cell axon. |
| axonal spine | A spine that originates from the axon, usually from the initial segment. |
| axonemal dynein complex | A dynein complex found in eukaryotic cilia and flagella; the motor domain heads interact with adjacent microtubules to generate a sliding force which is converted to a bending motion. May contain two or three dynein heavy chains as well as several light chains. |
| axonemal microtubule | A microtubule in the axoneme of a eukaryotic cilium or flagellum; an axoneme contains nine modified doublet microtubules, which may or may not surround a pair of single microtubules. |
| axoneme | The bundle of microtubules and associated proteins that forms the core of cilia (also called flagella) in eukaryotic cells and is responsible for their movements. |
| axoneme part | Any constituent part of an axoneme, the bundle of microtubules and associated proteins that forms the core of cilia (also called flagella) in eukaryotic cells and is responsible for their movements. |
| azurophil granule | Primary lysosomal granule found in neutrophil granulocytes. Contains a wide range of hydrolytic enzymes and is released into the extracellular fluid. |
| azurophil granule lumen | The volume enclosed by the membrane of an azurophil granule, a primary lysosomal granule found in neutrophil granulocytes that contains a wide range of hydrolytic enzymes and is released into the extracellular fluid. |
| b cell receptor complex | An immunoglobulin complex that is present in the plasma membrane of B cells and that in its canonical form is composed of two identical immunoglobulin heavy chains and two identical immunoglobulin light chains and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins. |
| baf-type complex | A SWI/SNF-type complex that contains a subunit from the BAF (Brahma-Associated Factor) family. |
| barr body | A structure found in a female mammalian cell containing an unpaired X chromosome that has become densely heterochromatic, silenced and localized at the nuclear periphery. |
| basal cortex | The region that lies just beneath the plasma membrane on the basal edge of a cell. |
| basal lamina | A thin sheet of proteoglycans and glycoproteins, especially laminin, secreted by cells as an extracellular matrix. |
| basal part of cell | The region of a cell situated near the base. For example, in a polarized epithelial cell, the basal surface rests on the basal lamina that separates the epithelium from other tissue. |
| basal plasma membrane | The region of the plasma membrane located at the basal end of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis. |
| basement membrane | A thin layer of dense material found in various animal tissues interposed between the cells and the adjacent connective tissue. It consists of the basal lamina plus an associated layer of reticulin fibers. |
| basement membrane collagen trimer | Any collagen timer that is part of a basement membrane. |
| basolateral plasma membrane | The region of the plasma membrane that includes the basal end and sides of the cell. Often used in reference to animal polarized epithelial membranes, where the basal membrane is the part attached to the extracellular matrix, or in plant cells, where the basal membrane is defined with respect to the zygotic axis. |
| bat3 complex | An ER membrane insertion complex that acts by facilitating tail-anchored protein capture by ASNA1/TRC40. In mammals the complex contains Bat3, TRC35 and Ubl4A. |
| bax complex | An oligomeric protein complex consisting of BAX, a member of the Bcl-2 family of anti- and proapoptotic regulators. |
| bbsome | A protein complex that associates with the primary cilium and is involved in cilium biogenesis; consists of seven conserved proteins: BBS1, BBS2, BBS4, BBS5, BBS7, BBS8 and BBS9. |
| bcl-2 family protein complex | A protein complex that consists of members of the Bcl-2 family of anti- and proapoptotic regulators. Bcl-2 proteins respond to cues from various forms of intracellular stress, such as DNA damage or cytokine deprivation, and interact with opposing family members to determine whether or not the caspase proteolytic cascade should be unleashed. |
| bcl3-bcl10 complex | A protein complex containing Bcl3 and Bcl10, which forms when Akt1 is activated by TNF-alpha to phosphorylate Bcl10; the Bcl3-Bcl10 complex is translocated to the nucleus. |
| bcl3/nf-kappab2 complex | A protein complex containing one Bcl protein and one or more copies of NF-kappaB2; formation of complexes of different stoichiometry depends on the Bcl3:NF-kappaB2 ratio, and allow Bcl3 to exert different regulatory effects on NF-kappaB2-dependent transcription. |
| beta-catenin destruction complex | A cytoplasmic protein complex containing glycogen synthase kinase-3-beta (GSK-3-beta), the adenomatous polyposis coli protein (APC), and the scaffolding protein axin, among others; phosphorylates beta-catenin, targets it for degradation by the proteasome. |
| beta-catenin-tcf7l2 complex | A protein complex that contains beta-catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription. |
| bim-bcl-2 complex | A heterodimeric protein complex consisting of BIM and BCL-2, members of the Bcl-2 family of anti- and proapoptotic regulators. |
| bim-bcl-xl complex | A heterodimeric protein complex consisting of BIM and BCL-xl, members of the Bcl-2 family of anti- and proapoptotic regulators. |
| bleb | A cell extension characterized by rapid formation, rounded shape, and scarcity of organelles within the protrusions. |
| bloc complex | Any of several protein complexes required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes, platelet dense granules, and other related organelles; acronym for biogenesis of lysosomal-related organelles complex. |
| bloc-1 complex | A protein complex required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes and platelet dense granules. Many of the protein subunits are conserved between mouse and human; the mouse complex contains the Pallidin, Muted, Cappuccino, Dysbindin, Snapin, BLOS1, BLOS2, AND BLOS3 proteins. |
| bloc-2 complex | A protein complex required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes and platelet dense granules. The human complex contains the Hps3, Hps5, and Hps6 proteins; the mouse complex contains ru2 and ru. |
| bloc-3 complex | A protein complex required for the biogenesis of specialized organelles of the endosomal-lysosomal system, such as melanosomes and platelet dense granules. The human complex contains the Hps1 and Hps4 proteins. |
| blood microparticle | A phospholipid microvesicle that is derived from any of several cell types, such as platelets, blood cells, endothelial cells, or others, and contains membrane receptors as well as other proteins characteristic of the parental cell. Microparticles are heterogeneous in size, and are characterized as microvesicles free of nucleic acids. |
| bounding membrane of organelle | The lipid bilayer that forms the outer-most layer of an organelle. |
| box c/d snornp complex | A ribonucleoprotein complex containing small nucleolar RNA of the box C/D type that can carry out ribose-2'-O-methylation of target RNAs. |
| box h/aca rnp complex | A ribonucleoprotein complex that contains an RNA of the box H/ACA type, a subtype of the small nucleolar RNA (snoRNA) family. RNA pseudouridylation (isomerization of uridine to pseudouridine) is the major, and most likely the ancestral, function of H/ACA RNPs, although some have evolved other functions. Pseudouridylation targets include both large and small ribosomal RNAs (rRNAs), and on U2 small nuclear RNA (U2 snRNA). |
| box h/aca snornp complex | A box H/ACA RNP complex that is located in the nucleolus. |
| brca1-a complex | A protein complex that contains the BRCA1-BARD1 heterodimer, RAP80/UIMC1, BRCC3/BRCC36, BRE/BRCC45, FAM175A/CCDC98/Abraxas and MERIT40/NBA1, and specifically recognizes and binds K63-linked polyubiquitin chains present on histone H2A and H2AX at DNA damage sites. |
| brca1-bard1 complex | A heterodimeric complex comprising BRCA1 and BARD1, which possesses ubiquitin ligase activity and is involved in genome maintenance, possibly by functioning in surveillance for DNA damage. |
| brca2-mage-d1 complex | A heterodimeric protein complex formed of BRCA2 and MAGE-D1; may mediate the synergistic activities of the two proteins in regulating cell growth. |
| brisc complex | A protein complex that contains the FAM175B/ABRO1, BRCC3/BRCC36, BRE/BRCC45 and MERIT40/NBA1 proteins, and specifically cleaves K63-linked polyubiquitin chains. |
| brush border | Dense covering of microvilli on the apical surface of epithelial cells in tissues such as the intestine, kidney, and choroid plexus; the microvilli aid absorption by increasing the surface area of the cell. |
| brush border membrane | The portion of the plasma membrane surrounding the brush border. |
| c zone | A region of the A band in which myosin-binding protein C is located and that can be seen by electron microscopy. This is a functional zone that also includes myosin. |
| c-fiber | The axon of a dorsal root ganglion cell that are responsive to pain and temperature. C-fibers are small in diameter (0.2-1.5 um) and unmyelinated. |
| caax-protein geranylgeranyltransferase complex | A heterodimeric enzyme, composed of an alpha and a beta subunit. Participates in the post-translational C-terminal modification of several small GTPases, allowing their targeting to the membrane. |
| caf-1 complex | A conserved heterotrimeric protein complex that promotes histone H3 and H4 deposition onto newly synthesized DNA during replication or DNA repair; specifically facilitates replication-dependent nucleosome assembly with the major histone H3 (H3.1). In many species the CAF-1 subunits are designated p150, p60, and p48. |
| cajal body | A class of nuclear body, first seen after silver staining by Ramon y Cajal in 1903, enriched in small nuclear ribonucleoproteins, and certain general RNA polymerase II transcription factors; ultrastructurally, they appear as a tangle of coiled, electron-dense threads roughly 0.5 micrometers in diameter; involved in aspects of snRNP biogenesis; the protein coilin serves as a marker for Cajal bodies. Some argue that Cajal bodies are the sites for preassembly of transcriptosomes, unitary particles involved in transcription and processing of RNA. |
| calcineurin complex | A heterodimeric calcium ion and calmodulin dependent protein phosphatase composed of catalytic and regulatory subunits; the regulatory subunit is very similar in sequence to calmodulin. |
| calcium channel complex | An ion channel complex through which calcium ions pass. |
| calcium ion-transporting atpase complex | Protein complex that carries out the reaction: ATP + H2O + Ca2+(out) = ADP + phosphate + Ca2+(in). |
| calcium- and calmodulin-dependent protein kinase complex | An enzyme complex which in eukaryotes is composed of four different chains: alpha, beta, gamma, and delta. The different isoforms assemble into homo- or heteromultimeric holoenzymes composed of 8 to 12 subunits. Catalyzes the phosphorylation of proteins to O-phosphoproteins. |
| camp-dependent protein kinase complex | An enzyme complex, composed of regulatory and catalytic subunits, that catalyzes protein phosphorylation. Inactive forms of the enzyme have two regulatory chains and two catalytic chains; activation by cAMP produces two active catalytic monomers and a regulatory dimer. |
| carboxy-terminal domain protein kinase complex | A protein complex that phosphorylates amino acid residues of RNA polymerase II C-terminal domain repeats; phosphorylation occurs mainly on Ser2 and Ser5. |
| catalytic complex | A protein complex which is capable of catalytic activity. |
| catalytic step 2 spliceosome | A spliceosomal complex that contains three snRNPs, including U5, bound to a splicing intermediate in which the first catalytic cleavage of the 5' splice site has occurred. The precise subunit composition differs significantly from that of the catalytic step 1, or activated, spliceosome, and includes many proteins in addition to those found in the associated snRNPs. |
| catenin complex | Complex of peripheral cytoplasmic proteins (alpha-, beta- and gamma-catenin) that interact with the cytoplasmic region of uvomorulin/E-cadherin to connect it to the actin cytoskeleton. |
| catenin-tcf7l2 complex | A protein complex that contains a catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription. |
| cation channel complex | An ion channel complex through which cations pass. |
| cation-transporting atpase complex | Protein complex that carries out the reaction: ATP + H2O + cation(out) = ADP + phosphate + cation(in). |
| catsper complex | A sperm-specific voltage-gated calcium channel that controls the intracellular calcium ion concentration and, thereby, the swimming behavior of sperm. Consists of a heteromeric tetramer surrounding a calcium ion- selective pore. May also contain additional auxiliary subunits. |
| caveola | A membrane raft that forms small pit, depression, or invagination that communicates with the outside of a cell and extends inward, indenting the cytoplasm and the cell membrane. Examples include any of the minute pits or incuppings of the cell membrane formed during pinocytosis. Such caveolae may be pinched off to form free vesicles within the cytoplasm. |
| caveolar macromolecular signaling complex | A complex composed of proteins required for beta adrenergic receptor activation of protein kinase A. It includes the Cav 12. subunit of L-type calcium channel, protein kinase A regulatory subunit 2(PKAR2), adenyl cyclase, beta-adrenergic receptor, G-alpha-S, protein phosphatase 2A (PP2A) and caveolin 3 (CAV3). |
| cbm complex | A protein complex comprising Carma1, Bcl10 and MALT1; plays a role in signal transduction during NF-kappaB activation. |
| ccaat-binding factor complex | A heteromeric transcription factor complex that binds to the CCAAT-box upstream of promoters; in Saccharomyces it activates the transcription of genes in response to growth in a nonfermentable carbon source; consists of four known subunits: HAP2, HAP3, HAP4 and HAP5. |
| ccr4-not complex | The evolutionarily conserved CCR4-NOT complex is involved in several aspects of mRNA metabolism, including repression and activation of mRNA initiation, control of mRNA elongation, and the deadenylation and subsequent degradation of mRNA. In Saccharomyces the CCR4-NOT complex comprises a core complex of 9 proteins (Ccr4p, Caf1p, Caf40p, Caf130p, Not1p, Not2p, Not3p, Not4p, and Not5p), Caf4p, Caf16p, and several less well characterized proteins. |
| cd40 receptor complex | A protein complex that contains at least CD40 (a cell surface receptor of the tumour necrosis factor receptor (TNFR) superfamily), and other signaling molecules. |
| cd95 death-inducing signaling complex | A protein complex formed upon binding of Fas/CD95/APO-1 to its ligand. The complex includes FADD/Mort1, procaspase-8/10 and c-FLIP in addition to the ligand-bound receptor. |
| cdc48p-npl4p-ufd1p aaa atpase complex | A multiprotein ATPase complex required for the efficient dislocation of ER-lumenal degradation substrates, and their subsequent proteolysis by the proteasome. In budding yeast, this complex includes Cdc48p, Npl4p and Ufd1p proteins. |
| cdc73/paf1 complex | A multiprotein complex that associates with RNA polymerase II and general RNA polymerase II transcription factor complexes and may be involved in both transcriptional initiation and elongation. In Saccharomyces the complex contains Paf1p, Cdc73p, Ctr9p, Rtf1p, and Leo1p. |
| cell | The basic structural and functional unit of all organisms. Includes the plasma membrane and any external encapsulating structures such as the cell wall and cell envelope. |
| cell body | The portion of a cell bearing surface projections such as axons, dendrites, cilia, or flagella that includes the nucleus, but excludes all cell projections. |
| cell body fiber | A neuron projection that is found in unipolar neurons and corresponds to the region between the cell body and the point at which the single projection branches. |
| cell body membrane | The plasma membrane of a cell that bears surface projections such as axons, dendrites, cilia, or flagella, excluding the plasma membrane on cell projections. |
| cell cortex | The region of a cell that lies just beneath the plasma membrane and often, but not always, contains a network of actin filaments and associated proteins. |
| cell cortex part | Any constituent part of the cell cortex, the region of a cell that lies just beneath the plasma membrane and often, but not always, contains a network of actin filaments and associated proteins. |
| cell division site | The eventual plane of cell division (also known as cell cleavage or cytokinesis) in a dividing cell. In Eukaryotes, the cleavage apparatus, composed of septin structures and the actomyosin contractile ring, forms along this plane, and the mitotic, or meiotic, spindle is aligned perpendicular to the division plane. In bacteria, the cell division site is generally located at mid-cell and is the site at which the cytoskeletal structure, the Z-ring, assembles. |
| cell division site part | Any constituent part of the cell division plane, the eventual plane of cell division in a dividing cell. |
| cell envelope | An envelope that surrounds a bacterial cell and includes the cytoplasmic membrane and everything external, encompassing the periplasmic space, cell wall, and outer membrane if present. |
| cell junction | A cellular component that forms a specialized region of connection between two cells or between a cell and the extracellular matrix. At a cell junction, anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells or to proteins in the extracellular matrix. |
| cell leading edge | The area of a motile cell closest to the direction of movement. |
| cell outer membrane | A lipid bilayer that forms the outermost membrane of the cell envelope; enriched in polysaccharide and protein; the outer leaflet of the membrane contains specific lipopolysaccharide structures. |
| cell part | Any constituent part of a cell, the basic structural and functional unit of all organisms. |
| cell periphery | The part of a cell encompassing the cell cortex, the plasma membrane, and any external encapsulating structures. |
| cell pole | Either of two different areas at opposite ends of an axis of a cell. |
| cell projection | A prolongation or process extending from a cell, e.g. a flagellum or axon. |
| cell projection cytoplasm | All of the contents of a cell projection, excluding the plasma membrane surrounding the projection. |
| cell projection membrane | The portion of the plasma membrane surrounding a cell surface projection. |
| cell projection part | Any constituent part of a cell projection, a prolongation or process extending from a cell, e.g. a flagellum or axon. |
| cell surface | The external part of the cell wall and/or plasma membrane. |
| cell surface furrow | A furrow that may be found on the cell surface. Examples are the cleavage furrow observed during cytokinesis in animal cells, and the cingulum and sulcus found in some dinoflagellates. |
| cell tip | The region at either end of the longest axis of a cylindrical or elongated cell. |
| cell trailing edge | The area of a motile cell opposite to the direction of movement. |
| cell trailing edge membrane | The portion of the plasma membrane surrounding the trailing edge of a motile cell. |
| cell wall | The rigid or semi-rigid envelope lying outside the cell membrane of plant, fungal, most prokaryotic cells and some protozoan parasites, maintaining their shape and protecting them from osmotic lysis. In plants it is made of cellulose and, often, lignin; in fungi it is composed largely of polysaccharides; in bacteria it is composed of peptidoglycan; in protozoan parasites such as Giardia species, it's made of carbohydrates and proteins. |
| cell-cell adherens junction | An adherens junction which connects a cell to another cell. |
| cell-cell contact zone | Extended zone of intimate apposition between two cells containing one or more types of intercellular junctions, e.g., the intercalated disk of muscle. |
| cell-cell junction | A cell junction that forms a connection between two cells; excludes direct cytoplasmic junctions such as ring canals. |
| cell-substrate adherens junction | An adherens junction which connects a cell to the extracellular matrix. |
| cell-substrate junction | A cell junction that forms a connection between a cell and the extracellular matrix. |
| cellular_component | The part of a cell or its extracellular environment in which a gene product is located. A gene product may be located in one or more parts of a cell and its location may be as specific as a particular macromolecular complex, that is, a stable, persistent association of macromolecules that function together. |
| central element | A structural unit of the synaptonemal complex found between the lateral elements. |
| centralspindlin complex | A heterotetrameric protein complex playing a key role in the formation of the central spindle in mitosis. Made up of two molecules each of a mitotic kinesin (ZEN-4 in Caenorhabditis elegans or MKLP1 in mammals) and of two molecules each of a GTPase activating protein (GAP) factor (CYK-4 in Caenorhabditis elegans or MgcRacGAP in mammals). |
| centriolar satellite | A small (70-100 nm) cytoplasmic granule that contains a number of centrosomal proteins; centriolar satellites traffic toward microtubule minus ends and are enriched near the centrosome. |
| centriole | A cellular organelle, found close to the nucleus in many eukaryotic cells, consisting of a small cylinder with microtubular walls, 300-500 nm long and 150-250 nm in diameter. It contains nine short, parallel, peripheral microtubular fibrils, each fibril consisting of one complete microtubule fused to two incomplete microtubules. Cells usually have two centrioles, lying at right angles to each other. At division, each pair of centrioles generates another pair and the twin pairs form the pole of the mitotic spindle. |
| centrosomal corona | An amorphous structure surrounding the core of the centrosome, from which microtubules are nucleated; contains gamma-tubulin. |
| centrosome | A structure comprised of a core structure (in most organisms, a pair of centrioles) and peripheral material from which a microtubule-based structure, such as a spindle apparatus, is organized. Centrosomes occur close to the nucleus during interphase in many eukaryotic cells, though in animal cells it changes continually during the cell-division cycle. |
| cerebellar mossy fiber | An axon arising from cerebellar projecting cells in the cochlea, vestibular nuclei, spinal cord, reticular formation, cerebellar nuclei and basilar pontine nuclei. Mossy fibers enter through all three cerebellar peduncles and send collaterals to the deep cerebellar nuclei, then branch in the white matter and terminate in the granule cell layer. Through this branching, a given mossy fiber can innervate several folia. Mossy fibers synapse on granule cells. The synaptic contacts are made at enlargements along the length of the mossy fiber called mossy fiber rosettes. The enlargements of the rosettes give the axons as mossy appearance in Golgi stained preparations. |
| cerf complex | An ISWI complex that contains an ATPase subunit of the ISWI family (specifically SNF2L in mammals, which contain two ISWI homologs) and a CECR2 homolog. In mammals, CERF is involved in regulation of transcription from RNA polymerase II promoters. |
| chaperonin-containing t-complex | A multisubunit ring-shaped complex that mediates protein folding in the cytosol without a cofactor. |
| chd-type complex | A SWI/SNF-type complex that contains a subunit from the CHD(Chromodomain helicase DNA-binding) family. The CHD family is characterized by two signature sequence motifs: tandem chromodomains located in the N-terminal region, and the SNF2-like ATPase domain located in the central region of the protein structure. |
| checkpoint clamp complex | Conserved heterotrimeric complex of PCNA-like proteins that is loaded onto DNA at sites of DNA damage. |
| chiasma | A connection formed between chromatids, visible during meiosis, thought to be the point of the interchange involved in crossing-over. |
| chitosome | An intracellular membrane-bounded particle found in fungi and containing chitin synthase; it synthesizes chitin microfibrils. Chitin synthase activity exists in chitosomes and they are proposed to act as a reservoir for regulated transport of chitin synthase enzymes to the division septum. |
| chloride channel complex | An ion channel complex through which chloride ions pass. |
| chrac | An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2H in mammals, Isw2 in S. cerevisiae), an ACF1 homolog, and additional small histone fold subunits (generally two of these, but Xenopus has only one and some additional non-conserved subunits). CHRAC plays roles in the regulation of RNA polymerase II transcription and in DNA replication and repair. |
| chromaffin granule | Specialized secretory vesicle found in the cells of adrenal glands and various other organs, which is concerned with the synthesis, storage, metabolism, and secretion of epinephrine and norepinephrine. |
| chromaffin granule lumen | The volume enclosed by the membrane of a chromaffin granule. |
| chromaffin granule membrane | The lipid bilayer surrounding a chromaffin granule, a specialized secretory vesicle found in the cells of adrenal glands and various other organs, which is concerned with the synthesis, storage, metabolism, and secretion of epinephrine and norepinephrine. |
| chromatin | The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome. |
| chromatin silencing complex | Any protein complex that mediates changes in chromatin structure that result in transcriptional silencing. |
| chromatoid body | A ribonucleoprotein complex found in the cytoplasm of male germ cells, composed of exceedingly thin filaments that are consolidated into a compact mass or into dense strands of varying thickness that branch to form an irregular network. Contains mRNAs, miRNAs, and protein components involved in miRNA processing (such as Argonaute proteins and the endonuclease Dicer) and in RNA decay (such as the decapping enzyme DCP1a and GW182). |
| chromocenter | A region in which centric, heterochromatic portions of one or more chromosomes form a compact structure. |
| chromosomal part | Any constituent part of a chromosome, a structure composed of a very long molecule of DNA and associated proteins (e.g. histones) that carries hereditary information. |
| chromosomal region | Any subdivision of a chromosome along its length. |
| chromosome | A structure composed of a very long molecule of DNA and associated proteins (e.g. histones) that carries hereditary information. |
| chromosome passenger complex | A eukaryotically conserved protein complex that localizes to kinetochores in early mitosis, the spindle mid-zone in anaphase B and to the telophase midbody. It has been proposed that the passenger complex coordinates various events based on its location to different structures during the course of mitosis. Complex members include the BIR-domain-containing protein Survivin, Aurora kinase, INCENP and Borealin. |
| chromosome, centromeric core domain | The innermost portion of the centromeric region of a chromosome, encompassing the core region of a chromosome centromere and the proteins that bind to it. |
| chromosome, centromeric region | The region of a chromosome that includes the centromeric DNA and associated proteins. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome. |
| chromosome, telomeric region | The terminal region of a linear chromosome that includes the telomeric DNA repeats and associated proteins. |
| chylomicron | A large lipoprotein particle (diameter 75-1200 nm) composed of a central core of triglycerides and cholesterol surrounded by a protein-phospholipid coating. The proteins include one molecule of apolipoprotein B-48 and may include a variety of apolipoproteins, including APOAs, APOCs and APOE. Chylomicrons are found in blood or lymph and carry lipids from the intestines into other body tissues. |
| chylomicron remnant | A lipoprotein particle that is derived from a mature chylomicron particle by the removal of triglycerides from the chylomicron core by lipoprotein lipase and the subsequent loss of surface components. It characteristically contains apolipoprotein E (APOE) and is cleared from the blood by the liver. |
| cia complex | The cytosolic iron-sulfur protein assembly (CIA) complex mediates the incorporation of iron-sulfur clusters into apoproteins involved in DNA metabolism and genomic integrity. |
| ciliary basal body | A membrane-tethered, short cylindrical array of microtubules and associated proteins found at the base of a eukaryotic cilium (also called flagellum) that is similar in structure to a centriole and derives from it. The cilium basal body is the site of assembly and remodelling of the cilium and serves as a nucleation site for axoneme growth. As well as anchoring the cilium, it is thought to provide a selective gateway regulating the entry of ciliary proteins and vesicles by intraflagellar transport. |
| ciliary cytoplasm | All of the contents of a cilium, excluding the plasma membrane surrounding the cilium. |
| ciliary membrane | The portion of the plasma membrane surrounding a cilium. |
| ciliary neurotrophic factor receptor complex | A protein complex that acts as a receptor for the cytokine ciliary neurotrophic factor (CNTF). In humans the receptor complex is a hexamer composed of two molecules each of CNTF and CNTFR and one molecule each of gp130 and LIFR. |
| ciliary part | Any constituent part of a cilium, a specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface. Each cilium is bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored basally in a centriole. |
| ciliary rootlet | A cytoskeleton-like structure, originating from the basal body at the proximal end of a cilium, and extending proximally toward the cell nucleus. Rootlets are typically 80-100 nm in diameter and contain cross striae distributed at regular intervals of approximately 55-70 nm. |
| ciliary transition zone | A region of the cilium between the basal body and proximal segment that is characterized by Y-shaped assemblages that connect axonemal microtubules to the ciliary membrane. The ciliary transition zone appears to function as a gate that controls ciliary membrane composition. |
| cilium | A specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface and of some cytoplasmic parts. Each cilium is largely bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored to a basal body. |
| cis-golgi network | The network of interconnected tubular and cisternal structures located at the convex side of the Golgi apparatus, which abuts the endoplasmic reticulum. |
| cis-golgi network membrane | The lipid bilayer surrounding any of the compartments that make up the cis-Golgi network. |
| citrate lyase complex | Citrate lyase is a multienzyme complex with three constituents: the alpha subunit, citrate-ACP transferase; the beta subunit, citryl-ACP lyase; and the gamma subunit, an acyl-carrier protein which also carries the prosthetic group components. All three subunits are required for citrate lyase enzyme activity. |
| clathrin adaptor complex | A membrane coat adaptor complex that links clathrin to a membrane. |
| clathrin coat | A membrane coat found on coated pits and some coated vesicles; consists of polymerized clathrin triskelions, each comprising three clathrin heavy chains and three clathrin light chains, linked to the membrane via one of the AP adaptor complexes. |
| clathrin coat of coated pit | The coat found on coated pits and the coated vesicles derived from coated pits; comprises clathrin and the AP-2 adaptor complex. |
| clathrin coat of endocytic vesicle | A clathrin coat found on an endocytic vesicle. |
| clathrin coat of trans-golgi network vesicle | A clathrin coat found on a vesicle of the trans-Golgi network. |
| clathrin complex | A protein complex that consists of three clathrin heavy chains and three clathrin light chains, organized into a symmetrical three-legged structure called a triskelion. In clathrin-coated vesicles clathrin is the main component of the coat and forms a polymeric mechanical scaffold on the vesicle surface. |
| clathrin vesicle coat | A clathrin coat found on a vesicle. |
| clathrin-coated endocytic vesicle | A clathrin-coated, membrane-bounded intracellular vesicle formed by invagination of the plasma membrane around an extracellular substance. |
| clathrin-coated endocytic vesicle membrane | The lipid bilayer surrounding a clathrin-coated endocytic vesicle. |
| clathrin-coated vesicle | A vesicle with a coat formed of clathrin connected to the membrane via one of the clathrin adaptor complexes. |
| clathrin-coated vesicle membrane | The lipid bilayer surrounding a clathrin-coated vesicle. |
| clathrin-sculpted acetylcholine transport vesicle | A clathrin-sculpted lipid bilayer membrane-enclosed vesicle after clathrin release and containing acetylcholine. |
| clathrin-sculpted acetylcholine transport vesicle membrane | The lipid bilayer surrounding a clathrin-sculpted acetylcholine transport vesicle. |
| clathrin-sculpted gamma-aminobutyric acid transport vesicle | A clathrin-sculpted lipid bilayer membrane-enclosed vesicle after clathrin release and containing gamma-aminobutyric acid transport vesicle. |
| clathrin-sculpted gamma-aminobutyric acid transport vesicle membrane | The lipid bilayer surrounding a clathrin-sculpted gamma-aminobutyric acid transport vesicle. |
| clathrin-sculpted glutamate transport vesicle | A clathrin-sculpted lipid bilayer membrane-enclosed vesicle after clathrin release and containing glutamate. |
| clathrin-sculpted glutamate transport vesicle membrane | The lipid bilayer surrounding a clathrin-sculpted glutamate transport vesicle. |
| clathrin-sculpted monoamine transport vesicle | A clathrin-sculpted lipid bilayer membrane-enclosed vesicle after clathrin release and containing monoamines. |
| clathrin-sculpted monoamine transport vesicle membrane | The lipid bilayer surrounding a clathrin-sculpted monoamine transport vesicle. |
| clathrin-sculpted vesicle | A clathrin-sculpted lipid bilayer membrane-enclosed vesicle after clathrin release. |
| cleavage body | A nuclear body that contains proteins involved in pre-mRNA 3'-end cleavage and polyadenylation, such as DDX1, CSTF2 and CPSFs, as well as the transcription factors TFIIE and TFIIF. Cleavage bodies are localized adjacent to Cajal bodies and are involved in mRNA3'-end processing. |
| cleavage furrow | In animal cells, the first sign of cleavage, or cytokinesis, is the appearance of a shallow groove in the cell surface near the old metaphase plate. A contractile ring containing actin and myosin is located just inside the plasma membrane at the location of the furrow. Ring contraction is associated with centripetal growth of the membrane that deepens the cleavage furrow and divides the cytoplasm of the two daughter cells. While the term 'cleavage furrow' was initially associated with animal cells, such a structure occurs in many other types of cells, including unicellular protists. |
| climbing fiber | The axon of inferior olive neuron that projects to the cerebellar cortex, largely via the inferior cerebellar peduncle. They range in diameter from 1-3 um and are myelinated until they enter the granule cell layer. They give off collaterals to the deep cerebellar nuclei. They synapse extensively with the dendrites of Purkinje cells in the molecular layer, where each fiber branches repeatedly to climb along the Purkinje cell dendritic tree. Each Purkinje cell is innervated by only a single climbing fiber. |
| cntfr-clcf1 complex | A protein complex that is composed of two soluble ciliary neurotrophic factor receptor alpha subunits (product of the CNTFR gene) and two molecules of cardiotrophin-like cytokine factor 1 (product of the CLCF1 gene). The complex is secreted into the extracellular space. |
| coated membrane | A single or double lipid bilayer with any of several different proteinaceous coats that can associate with membranes. Membrane coats include those formed by clathrin plus an adaptor complex, the COPI and COPII complexes. |
| coated pit | A part of the endomembrane system in the form of an invagination of a membrane upon which a clathrin coat forms, and that can be converted by vesicle budding into a clathrin-coated vesicle. Coated pits form on the plasma membrane, where they are involved in receptor-mediated selective transport of many proteins and other macromolecules across the cell membrane, in the trans-Golgi network, and on some endosomes. |
| coated vesicle | Small membrane-bounded organelle formed by pinching off of a coated region of membrane. Some coats are made of clathrin, whereas others are made from other proteins. |
| coated vesicle membrane | The lipid bilayer surrounding a coated vesicle. |
| cohesin complex | A protein complex that is required for sister chromatid cohesion in eukaryotes. The cohesin complex forms a molecular ring complex, and is composed of structural maintenance of chromosomes (SMC) and kleisin proteins. For example, in yeast, the complex is composed of the SMC proteins Smc1p and Smc3p, and the kleisin protein Scc1p. In vertebrates, the complex is composed of the SMC1 (SMC1A or SMC1B) and SMC3 heterodimer attached via their hinge domains to a kleisin (RAD21, REC8 or RAD21L) which links them, and one STAG protein (STAG1, STAG2 or STAG3). |
| cohesin core heterodimer | The core heterodimer of a cohesin complex; a structure required for sister chromatid cohesion in eukaryotes. |
| collagen trimer | A protein complex consisting of three collagen chains assembled into a left-handed triple helix. These trimers typically assemble into higher order structures. |
| collagen type i trimer | A collagen trimer containing alpha(I) chains. The most common form of type I collagen is a heterotrimer containing two alpha1(I) chains and one alpha2(I) chain; homotrimers containing three alpha1(I) chains are also found. Type I collagen triple helices associate to form banded fibrils. |
| collagen type ii trimer | A collagen homotrimer of alpha1(II) chains; type II collagen triple helices associate to form fibrils. |
| collagen type iii trimer | A collagen homotrimer of alpha1(III) chains; type III collagen triple helices associate to form fibrils. |
| collagen type iv trimer | A collagen heterotrimer containing type IV alpha chains; [alpha1(IV)]2alpha2(IV) trimers are commonly observed, although more type IV alpha chains exist and may be present in type IV trimers; type IV collagen triple helices associate to form 3 dimensional nets within basement membranes. |
| collagen type ix trimer | A collagen heterotrimer containing type IX alpha chains in alpha1(IX)alpha2(IX)alpha3(IX) trimers; type IX collagen triple helices associate to form a structure that links glycosaminoglycans to type II collagen fibrils. |
| collagen type v trimer | A collagen heterotrimer containing type V alpha chains; [alpha1(V)]2alpha2(V) and alpha1(V)alpha2(V)alpha3(V) trimers have been observed; type V collagen triple helices associate to form fibrils. |
| collagen type vi trimer | A collagen heterotrimer containing type VI alpha chains in alpha1(VI)alpha2(VI)alpha3(VI) trimers; type VI collagen triple helices associate to form beaded fibrils. |
| collagen type vii trimer | A collagen homotrimer of alpha1(VII) chains; type VII collagen triple helices form antiparallel dimer, which in turn associate laterally to form anchoring fibrils that connect type IV collagen in the basal lamina to plaques in the underlying connective tissue. It binds laminin. |
| collagen type viii trimer | A collagen heterotrimer containing type VIII alpha chains; [alpha1(VIII)2]alpha2(VIII) and alpha1(VIII)[alpha2(VIII)]2 trimers have been observed; type VIII collagen triple helices associate to form regular hexagonal nets. |
| collagen type xi trimer | A collagen heterotrimer containing type XI alpha chains in alpha1(XI)alpha2(XI)alpha3(XI) trimers; type XI collagen triple helices associate to form fibrils. |
| collagen type xii trimer | A collagen homotrimer of alpha1(XII) chains; type XII collagen triple helices may link sheet-forming or fibrillar collagens to other structures. |
| collagen type xiii trimer | A collagen homotrimer of alpha1(XIII) chains; type XIII collagen triple helices span the plasma membrane. |
| collagen type xiv trimer | A collagen homotrimer of alpha1(XIV) chains; type XIV collagen triple helices may link sheet-forming or fibrillar collagens to other structures. |
| collagen type xv trimer | A collagen homotrimer of alpha1(XV) chains; a chondroitin sulfate proteoglycan often found in specialized basement membranes where it bridges between fibrils. |
| collagen type xvi trimer | A collagen trimer containing alpha(XVI) chains; type XVI trimers can associate with microfibrils. |
| commitment complex | A spliceosomal complex that is formed by association of the U1 snRNP with the 5' splice site of an unspliced intron in an RNA transcript. |
| compact myelin | The portion of the myelin sheath in which layers of cell membrane are tightly juxtaposed, completely excluding cytoplasm. The juxtaposed cytoplasmic surfaces form the major dense line, while the juxtaposed extracellular surfaces form the interperiod line visible in electron micrographs. |
| complement component c1 complex | A protein complex composed of six subunits of C1q, each formed of the three homologous polypeptide chains C1QA, C1QB, and C1QB, and tetramer of two C1QR and two C1QS polypeptide chains. |
| condensed chromosome | A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct structure. |
| condensed chromosome inner kinetochore | The region of a condensed chromosome kinetochore closest to centromeric DNA; in mammals the CREST antigens (CENP proteins) are found in this layer; this layer may help define underlying centromeric chromatin structure and position of the kinetochore on the chromosome. |
| condensed chromosome kinetochore | A multisubunit complex that is located at the centromeric region of a condensed chromosome and provides an attachment point for the spindle microtubules. |
| condensed chromosome outer kinetochore | The region of a condensed chromosome kinetochore most external to centromeric DNA; this outer region mediates kinetochore-microtubule interactions. |
| condensed chromosome, centromeric region | The region of a condensed chromosome that includes the centromere and associated proteins, including the kinetochore. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome. |
| condensed nuclear chromosome | A highly compacted molecule of DNA and associated proteins resulting in a cytologically distinct structure that remains in the nucleus. |
| condensed nuclear chromosome kinetochore | A multisubunit complex that is located at the centromeric region of a condensed chromosome in the nucleus and provides an attachment point for the spindle microtubules. |
| condensed nuclear chromosome outer kinetochore | The region of a condensed nuclear chromosome kinetochore most external to centromeric DNA; this outer region mediates kinetochore-microtubule interactions. |
| condensed nuclear chromosome, centromeric region | The region of a condensed chromosome in the nucleus that includes the centromere and associated proteins, including the kinetochore. In monocentric chromosomes, this region corresponds to a single area of the chromosome, whereas in holocentric chromosomes, it is evenly distributed along the chromosome. |
| condensin complex | A multisubunit protein complex that plays a central role in chromosome condensation. |
| condensin core heterodimer | The core heterodimer of a condensin complex, a multisubunit protein complex that plays a central role in chromosome condensation. |
| cone cell pedicle | A specialized axon terminus which is produced by retinal cone cells. Pedicles are large, conical, flat end-feet (8-10 micrometers diameter) of the retinal cone axon that lie more or less side by side on the same plane at the outer edge of the outer plexiform layer (OPL). |
| connexon complex | An assembly of six molecules of connexin, made in the Golgi apparatus and subsequently transported to the plasma membrane, where docking of two connexons on apposed plasma membranes across the extracellular space forms a gap junction. |
| contractile fiber | Fibers, composed of actin, myosin, and associated proteins, found in cells of smooth or striated muscle. |
| contractile fiber part | Any constituent part of a contractile fiber, a fiber composed of actin, myosin, and associated proteins, found in cells of smooth or striated muscle. |
| contractile ring | A cytoskeletal structure composed of filamentous protein that forms beneath the membrane of many cells or organelles, in the plane of cell or organelle division. Ring contraction is associated with centripetal growth of the membrane that divides the cytoplasm of the two daughter cells or organelles. |
| cop9 signalosome | A protein complex that catalyzes the deneddylation of proteins, including the cullin component of SCF ubiquitin E3 ligase; deneddylation increases the activity of cullin family ubiquitin ligases. The signalosome is involved in many regulatory process, including some which control development, in many species; also regulates photomorphogenesis in plants; in many species its subunits are highly similar to those of the proteasome. |
| copi vesicle coat | One of two multimeric complexes that forms a membrane vesicle coat. The mammalian COPI subunits are called alpha-, beta-, beta'-, gamma-, delta-, epsilon- and zeta-COP. Vesicles with COPI coats are found associated with Golgi membranes at steady state. |
| copi-coated vesicle | A vesicle with a coat formed of the COPI coat complex proteins. COPI-coated vesicles are found associated with Golgi membranes at steady state, are involved in Golgi to endoplasmic reticulum (retrograde) vesicle transport, and possibly also in intra-Golgi transport. |
| copi-coated vesicle membrane | The lipid bilayer surrounding a COPI-coated vesicle. |
| copii vesicle coat | One of two multimeric complexes that forms a membrane vesicle coat. COPII is best characterized in S. cerevisiae, where the subunits are called Sar1p, Sec13p, Sec31p, Sec23p, and Sec24p. Vesicles with COPII coats are found associated with endoplasmic reticulum (ER) membranes at steady state. |
| core tfiih complex | The 7 subunit core of TFIIH that is a part of either the general transcription factor holo-TFIIH or the nucleotide-excision repair factor 3 complex. In S. cerevisiae/humans the complex is composed of: Ssl2/XPB, Tfb1/p62, Tfb2/p52, Ssl1/p44, Tfb4/p34, Tfb5/p8 and Rad3/XPD. |
| cornified envelope | A type of plasma membrane that has been modified through addition of distinct intracellular and extracellular components, including ceramide, found in cornifying epithelial cells (corneocytes). |
| cortical actin cytoskeleton | The portion of the actin cytoskeleton, comprising filamentous actin and associated proteins, that lies just beneath the plasma membrane. |
| cortical cytoskeleton | The portion of the cytoskeleton that lies just beneath the plasma membrane. |
| cortical endoplasmic reticulum | A cortical network of highly dynamic tubules that are juxtaposed to the plasma membrane and undergo ring closure and tubule-branching movements. |
| cortical granule | A secretory vesicle that is stored under the cell membrane of an egg. These vesicles fuse with the egg plasma membrane as part of egg activation and are part of the block to polyspermy. |
| cortical microtubule cytoskeleton | The portion of the microtubule cytoskeleton that lies just beneath the plasma membrane. |
| costamere | Regular periodic sub membranous arrays of vinculin in skeletal and cardiac muscle cells, these arrays link Z-discs to the sarcolemma and are associated with links to extracellular matrix. |
| crd-mediated mrna stability complex | A protein complex that binds to, and promotes stabilization of, mRNA molecules containing the coding region instability determinant (CRD). In human, IGF2BP1 and at least four additional proteins: HNRNPU, SYNCRIP, YBX1, and DHX9. |
| crlf-clcf1 complex | A heterodimeric protein complex that is composed of cardiotrophin-like cytokine factor 1 (product of the CLCF1 gene) and cytokine receptor-like factor 1 (product of the CRLF gene) and is secreted into the extracellular space. The CRLF-CLCF1 complex is a ligand for the ciliary neurotrophic factor (CNTF) receptor complex. |
| cul2-ring ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul2 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an elongin-BC adaptor and a SOCS/BC box protein. |
| cul3-ring ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul3 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a BTB-domain-containing protein. |
| cul4-ring e3 ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul4 family and a RING domain protein form the catalytic core; substrate specificity is conferred by an adaptor protein. |
| cul4a-ring e3 ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul4A subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an adaptor protein. |
| cul4b-ring e3 ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul4B subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by unknown subunits. |
| cul5-ring ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul5 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by an elongin-BC adaptor and a SOCS/BC box protein. |
| cul7-ring ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul7 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a Skp1 linker and an F-box protein. |
| cullin-ring ubiquitin ligase complex | Any ubiquitin ligase complex in which the catalytic core consists of a member of the cullin family and a RING domain protein; the core is associated with one or more additional proteins that confer substrate specificity. |
| cuticular plate | A dense network of actin filaments found beneath the apical cell surface of hair cells, and into which stereocilia are inserted. |
| cyclin k-cdk12 complex | A protein complex consisting of cyclin Kand cyclin-dependent kinase 12 (CDK12). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner. |
| cyclin k-cdk13 complex | A protein complex consisting of cyclin Kand cyclin-dependent kinase 13 (CDK13). Cyclins are characterized by periodicity in protein abundance throughout the cell cycle. Cyclin-dependent kinases represent a family of serine/threonine protein kinases that become active upon binding to a cyclin regulatory partner. |
| cyclin-dependent protein kinase 5 holoenzyme complex | A protein complex that activates cyclin-dependent kinase 5; composed of regulatory and catalytic subunits. |
| cyclin-dependent protein kinase activating kinase holoenzyme complex | A cyclin-dependent kinase activating kinase complex capable of activating cyclin-dependent kinases by threonine phosphorylation, thus regulating cell cycle progression. consists of a kinase, cyclin and optional assembly factors, in human CDK7, CCNH and MNAT1. CAK activity is itself regulated throughout the cell cycle by T-loop phosphorylation of its kinase component (CDK7 in human). Phosphorylation of serine residues during mitosis inactivates the enzyme. Also capable of CAK phosphorylating the carboxyl-terminal domain (CTD) of RNA polymerase II and other transcription activating proteins, as part of the general transcription factor TFIIH. |
| cyclin-dependent protein kinase holoenzyme complex | Cyclin-dependent protein kinases (CDKs) are enzyme complexes that contain a kinase catalytic subunit associated with a regulatory cyclin partner. |
| cytochrome complex | A protein complex in which at least one of the proteins is a cytochrome, i.e. a heme-containing protein involved in catalysis of redox reactions. |
| cytolytic granule | A specialized secretory lysosome that is present in cells with cytolytic capability such as cytotoxic T lymphocytes and natural killer cells. Cytolytic granules mediate the storage and regulated excretion of lytic molecules for killing of target cells. |
| cytoplasm | All of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures. |
| cytoplasmic chromatin | The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome in the cytoplasm. |
| cytoplasmic chromosome | A chromosome found in the cytoplasm. |
| cytoplasmic cyclin-dependent protein kinase holoenzyme complex | Cyclin-dependent protein kinase (CDK) complex found in the cytoplasm. |
| cytoplasmic dynein complex | Any dynein complex that catalyzes movement along a cytoplasmic microtubule; cytoplasmic dynein complexes participates in many transport activities in eukaryotes, such as mRNA localization, intermediate filament transport, nuclear envelope breakdown, apoptosis, transport of centrosomal proteins, mitotic spindle assembly, virus transport, kinetochore functions, and movement of signaling and spindle checkpoint proteins. Subunits associated with the dynein heavy chain mediate association between dynein heavy chain and cargoes,and may include light chains and light intermediate chains. |
| cytoplasmic exosome (rnase complex) | Complex of 3'-5' exoribonucleases found in the cytoplasm. |
| cytoplasmic membrane-bounded vesicle | A membrane-bounded vesicle found in the cytoplasm of the cell. |
| cytoplasmic membrane-bounded vesicle lumen | The volume enclosed by the membrane of a cytoplasmic membrane-bounded vesicle. |
| cytoplasmic microtubule | Any microtubule in the cytoplasm of a cell. |
| cytoplasmic mrna processing body | A focus in the cytoplasm where mRNAs may become inactivated by decapping or some other mechanism. mRNA processing and binding proteins are localized to these foci. |
| cytoplasmic part | Any constituent part of the cytoplasm, all of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures. |
| cytoplasmic ribonucleoprotein granule | A ribonucleoprotein granule located in the cytoplasm. |
| cytoplasmic side of membrane | The side of a membrane that faces the cytoplasm. |
| cytoplasmic side of mitochondrial outer membrane | The external (cytoplasmic) face of the mitochondrial outer membrane. |
| cytoplasmic side of plasma membrane | The leaflet the plasma membrane that faces the cytoplasm and any proteins embedded or anchored in it or attached to its surface. |
| cytoplasmic stress granule | A dense aggregation in the cytosol composed of proteins and RNAs that appear when the cell is under stress. |
| cytoplasmic ubiquitin ligase complex | A ubiquitin ligase complex found in the cytoplasm. |
| cytoplasmic vesicle | A vesicle formed of membrane or protein, found in the cytoplasm of a cell. |
| cytoplasmic vesicle membrane | The lipid bilayer surrounding a cytoplasmic vesicle. |
| cytoplasmic vesicle part | Any constituent part of cytoplasmic vesicle, a vesicle formed of membrane or protein, found in the cytoplasm of a cell. |
| cytoplasmic viral factory | A viral factory located in the cytoplasm of a host cell. |
| cytoskeletal calyx | A large cytoskeletal structure located at the posterior end of the perinuclear theca of a mammalian sperm head. The nucleus is tightly associated with the calyx, which contains calicin and basic cylicin proteins. |
| cytoskeletal part | Any constituent part of the cytoskeleton, a cellular scaffolding or skeleton that maintains cell shape, enables some cell motion (using structures such as flagella and cilia), and plays important roles in both intra-cellular transport (e.g. the movement of vesicles and organelles) and cellular division. Includes constituent parts of intermediate filaments, microfilaments, microtubules, and the microtrabecular lattice. |
| cytoskeleton | Any of the various filamentous elements that form the internal framework of cells, and typically remain after treatment of the cells with mild detergent to remove membrane constituents and soluble components of the cytoplasm. The term embraces intermediate filaments, microfilaments, microtubules, the microtrabecular lattice, and other structures characterized by a polymeric filamentous nature and long-range order within the cell. The various elements of the cytoskeleton not only serve in the maintenance of cellular shape but also have roles in other cellular functions, including cellular movement, cell division, endocytosis, and movement of organelles. |
| cytosol | The part of the cytoplasm that does not contain organelles but which does contain other particulate matter, such as protein complexes. |
| cytosolic aryl hydrocarbon receptor complex | An aryl hydrocarbon receptor complex found in the cytosol, in which the ligand-binding subunit AhR is not bound to ligand; consists of AhR, two molecules of HSP90, the protein kinase c-Src, and the immunophilin XAP2/AIP. |
| cytosolic large ribosomal subunit | The large subunit of a ribosome located in the cytosol. |
| cytosolic part | Any constituent part of cytosol, that part of the cytoplasm that does not contain membranous or particulate subcellular components. |
| cytosolic proteasome complex | A proteasome complex found in the cytosol of a cell. |
| cytosolic ribosome | A ribosome located in the cytosol. |
| cytosolic small ribosomal subunit | The small subunit of a ribosome located in the cytosol. |
| dbird complex | A protein complex that associates with mRNP particles and RNA polymerase II and is proposed to integrate transcript elongation with the regulation of alternative splicing. In humans it is composed of the proteins KIAA1967/DBC1 and ZNF326/ZIRD. |
| death-inducing signaling complex | A protein complex formed by the association of signaling proteins with a death receptor upon ligand binding. The complex includes procaspases and death domain-containing proteins in addition to the ligand-bound receptor, and may control the activation of caspases 8 and 10. |
| delta dna polymerase complex | A multimeric DNA polymerase enzyme complex which differs in composition amongst species; in humans it is a heterotetramer of four subunits of approximately 125, 50, 68 and 12kDa, while in S. cerevisiae, it has three different subunits which form a heterotrimer, and the active enzyme is a dimer of this heterotrimer. Functions in DNA replication, mismatch repair and excision repair. |
| dendrite | A neuron projection that has a short, tapering, often branched, morphology, receives and integrates signals from other neurons or from sensory stimuli, and conducts a nerve impulse towards the axon or the cell body. In most neurons, the impulse is conveyed from dendrites to axon via the cell body, but in some types of unipolar neuron, the impulse does not travel via the cell body. |
| dendrite cytoplasm | All of the contents of a dendrite, excluding the surrounding plasma membrane. |
| dendrite membrane | The portion of the plasma membrane surrounding a dendrite. |
| dendrite terminus | A structure at the distal end of a dendrite adapted to carry out a specific function, e.g. dendriole. |
| dendritic growth cone | The migrating motile tip of a growing nerve cell dendrite. |
| dendritic shaft | Cylindric portion of the dendrite, directly stemming from the perikaryon, and carrying the dendritic spines. |
| dendritic spine | Protrusion from a dendrite. Spines are specialised subcellular compartments involved in the synaptic transmission. They are linked to the dendritic shaft by a restriction. Because of their bulb shape, they function as a biochemical and an electrical compartment. Spine remodeling is though to be involved in synaptic plasticity. |
| dendritic spine head | Distal part of the dendritic spine, that carries the post-synaptic density. |
| dendritic spine membrane | The portion of the plasma membrane surrounding a dendritic spine. |
| dendritic spine neck | Part of the dendritic spine that connects the dendritic shaft to the head of the dendritic spine. |
| dense body | An electron dense body which may contain granules. |
| dense core granule | Electron-dense organelle with a granular internal matrix; contains proteins destined to be secreted. |
| dense core granule membrane | The lipid bilayer surrounding a dense core granule. |
| dentate gyrus mossy fiber | Distinctive, unmyelinated axons produced by granule cells. |
| desmosome | A cell-cell junction in which: on the cytoplasmic surface of each interacting plasma membrane is a dense plaque composed of a mixture of intracellular anchor proteins; a bundle of keratin intermediate filaments is attached to the surface of each plaque; transmembrane adhesion proteins of the cadherin family bind to the plaques and interact through their extracellular domains to hold the adjacent membranes together by a Ca2+-dependent mechanism. |
| dihydrolipoyl dehydrogenase complex | A protein complex that possesses alpha-ketoglutarate dehydrogenase activity. |
| dimeric iga immunoglobulin complex | A protein complex composed of two monomeric IgA immunoglobulin complexes linked through both direct disulfide bonds and through a disulfide binded monomer of J chain acting as a bridge. Each IgA monomer consists of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds. Dimeric IgA is sometimes complexed additionally with secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| discoidal high-density lipoprotein particle | A newly formed high-density lipoprotein particle; consists of a phospholipid bilayer surrounded by two or more APOA1 molecules. The discoidal HDL particle is formed when lipid-free or lipid-poor APOA1 acquires phospholipids and unesterified cholesterol from either cell membranes or triglyceride-rich lipoproteins (undergoing lipolysis by lipoprotein lipase). |
| dna bending complex | A protein-DNA complex that contains DNA in combination with a protein which binds to and bends DNA. Often plays a role in DNA compaction. |
| dna helicase complex | A protein complex that possesses DNA helicase activity. |
| dna ligase iv complex | A eukaryotically conserved protein complex that contains DNA ligase IV and is involved in DNA repair by non-homologous end joining; in addition to the ligase, the complex also contains XRCC4 or a homolog, e.g. Saccharomyces Lif1p. |
| dna packaging complex | A protein complex that plays a role in the process of DNA packaging. |
| dna polymerase complex | A protein complex that possesses DNA polymerase activity and is involved in template directed synthesis of DNA. |
| dna polymerase iii complex | The DNA polymerase III holoenzyme is a complex that contains 10 different types of subunits. These subunits are organized into 3 functionally essential sub-assemblies: the pol III core, the beta sliding clamp processivity factor and the clamp-loading complex. The pol III core carries out the polymerase and the 3'-5' exonuclease proofreading activities. The polymerase is tethered to the template via the sliding clamp processivity factor. The clamp-loading complex assembles the beta processivity factor onto the primer template and plays a central role in the organization and communication at the replication fork. |
| dna polymerase processivity factor complex | A protein complex which is capable of increasing the processivity of nucleotide polymerization by DNA polymerase as a part of DNA replication. |
| dna recombinase mediator complex | A protein complex containing accessory proteins which bind a recombinase (e.g. Rad51) and bind single-stranded DNA (ssDNA), and promote nucleation of the recombinase onto ssDNA. |
| dna repair complex | A protein complex involved in DNA repair processes including direct reversal, base excision repair, nucleotide excision repair, photoreactivation, bypass, double-strand break repair pathway, and mismatch repair pathway. |
| dna replication factor a complex | A conserved heterotrimeric complex that binds nonspecifically to single-stranded DNA and is required for multiple processes in eukaryotic DNA metabolism, including DNA replication, DNA repair, and recombination. In all eukaryotic organisms examined the complex is composed of subunits of approximately 70, 30, and 14 kDa. |
| dna replication factor c complex | A complex of five polypeptides in eukaryotes, and two in prokaryotes, that loads the DNA polymerase processivity factor proliferating cell nuclear antigen (PCNA) onto DNA, thereby permitting processive DNA synthesis catalyzed by DNA polymerase. |
| dna topoisomerase complex (atp-hydrolyzing) | Complex that possesses DNA topoisomerase (ATP-hydrolyzing) activity. |
| dna-dependent protein kinase-dna ligase 4 complex | A large protein complex which is involved in the repair of DNA double-strand breaks and, in mammals, V(D)J recombination events. It consists of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), the DNA end-binding heterodimer Ku, the nuclear phosphoprotein XRCC4 or a homolog thereof, and DNA ligase IV. |
| dna-directed rna polymerase complex | A protein complex that possesses DNA-directed RNA polymerase activity. |
| dna-directed rna polymerase i complex | RNA polymerase I, one of three nuclear DNA-directed RNA polymerases found in all eukaryotes, is a multisubunit complex; typically it produces rRNAs. Two large subunits comprise the most conserved portion including the catalytic site and share similarity with other eukaryotic and bacterial multisubunit RNA polymerases. The remainder of the complex is composed of smaller subunits (generally ten or more), some of which are also found in RNA polymerase III and others of which are also found in RNA polymerases II and III. Although the core is competent to mediate ribonucleic acid synthesis, it requires additional factors to select the appropriate template. |
| dna-directed rna polymerase ii, core complex | RNA polymerase II, one of three nuclear DNA-directed RNA polymerases found in all eukaryotes, is a multisubunit complex; typically it produces mRNAs, snoRNAs, and some of the snRNAs. Two large subunits comprise the most conserved portion including the catalytic site and share similarity with other eukaryotic and bacterial multisubunit RNA polymerases. The largest subunit of RNA polymerase II contains an essential carboxyl-terminal domain (CTD) composed of a variable number of heptapeptide repeats (YSPTSPS). The remainder of the complex is composed of smaller subunits (generally ten or more), some of which are also found in RNA polymerases I and III. Although the core is competent to mediate ribonucleic acid synthesis, it requires additional factors to select the appropriate template. |
| dna-directed rna polymerase ii, holoenzyme | Large protein complex composed of the RNA polymerase core complex and a variety of other proteins including transcription factor complexes TFIIA, D, E, F, and H which are required for promoter recognition, and the Mediator subcomplex. Catalyzes the synthesis of eukaryotic pre-mRNA. |
| dna-directed rna polymerase iii complex | RNA polymerase III, one of three nuclear DNA-directed RNA polymerases found in all eukaryotes, is a multisubunit complex; typically it produces 5S rRNA, tRNAs and some of the small nuclear RNAs. Two large subunits comprise the most conserved portion including the catalytic site and share similarity with other eukaryotic and bacterial multisubunit RNA polymerases. The remainder of the complex is composed of smaller subunits (generally ten or more), some of which are also found in RNA polymerase I and others of which are also found in RNA polymerases I and II. Although the core is competent to mediate ribonucleic acid synthesis, it requires additional factors to select the appropriate template. |
| dolichol-phosphate-mannose synthase complex | A protein complex that possesses dolichyl-phosphate beta-D-mannosyltransferase activity; contains a catalytic subunit, a regulatory subunit, and a third subunit that stabilizes the complex. In human and several other metazoa, the subunits are named DPM1, DPM2 and DPM3, respectively. |
| drm complex | A transcriptional repressor complex that contains the lin-9, lin-35, lin-37, lin-52, lin-53, lin-5is involved in 4-, dpl-1 and efl-1 proteins, and is involved in cell fate specification. |
| dsif complex | A heterodimeric protein complex formed of Spt4 and Spt5 proteins which is expressed in eukaryotes from yeast to man. DSIF is an inhibitory elongation factor that promotes RNA polymerase II transcriptional pausing, but can also stimulate transcriptional elongation under certain conditions, and may play a role in RNA processing via its physical association with mRNA capping enzymes. |
| dubm complex | A protein complex that forms part of SAGA-type complexes SAGA and SLIK, and mediates deubiquitination of histone H2B. In S. cerevisiae, the DUBm consists of the proteins Ubp8p, Sgf11p, Sus1p, and Sgf73p. |
| dynactin complex | A 20S multiprotein assembly of total mass about 1.2 MDa that activates dynein-based activity in vivo. A large structural component of the complex is an actin-like 40 nm filament composed of actin-related protein, to which other components attach. |
| dynein complex | Any of several large complexes that contain two or three dynein heavy chains and several light chains, and have microtubule motor activity. |
| dystroglycan complex | A protein complex that includes alpha- and beta-dystroglycan, which are alternative products of the same gene; the laminin-binding component of the dystrophin-associated glycoprotein complex, providing a link between the subsarcolemmal cytoskeleton (in muscle cells) and the extracellular matrix. Alpha-dystroglycan is an extracellular protein binding to alpha-laminin and to beta-dystroglycan; beta-dystroglycan is a transmembrane protein which binds alpha-dystroglycan and dystrophin. |
| dystrophin-associated glycoprotein complex | A multiprotein complex that forms a strong mechanical link between the cytoskeleton and extracellular matrix; typical of, but not confined to, muscle cells. The complex is composed of transmembrane, cytoplasmic, and extracellular proteins, including dystrophin, sarcoglycans, dystroglycan, dystrobrevins, syntrophins, sarcospan, caveolin-3, and NO synthase. |
| early endosome | A membrane-bounded organelle that receives incoming material from primary endocytic vesicles that have been generated by clathrin-dependent and clathrin-independent endocytosis; vesicles fuse with the early endosome to deliver cargo for sorting into recycling or degradation pathways. |
| early endosome lumen | The volume enclosed by the membrane of an early endosome. |
| early endosome membrane | The lipid bilayer surrounding an early endosome. |
| early phagosome | A membrane-bounded intracellular vesicle as initially formed upon the ingestion of particulate material by phagocytosis. |
| ectoplasm | Granule free cytoplasm, lying immediately below the plasma membrane. |
| egg coat | A specialized extracellular matrix that surrounds the ovum of animals. The egg coat provides structural support and can play an essential role in oogenesis, fertilization and early development. |
| elastic fiber | An extracellular matrix part that consists of an insoluble core of polymerized tropoelastin monomers and a surrounding mantle of microfibrils. Elastic fibers provide elasticity and recoiling to tissues and organs, and maintain structural integrity against mechanical strain. |
| ell-eaf complex | A heterodimeric protein complex that acts as an RNA polymerase II elongation factor; the complex is conserved from yeast to humans, and is present in S. pombe, but absent from S. cerevisiae. |
| elongator holoenzyme complex | A heterohexameric protein complex that is involved in modification of wobble nucleosides in tRNA, and exerts direct effects on transcriptional elongation and exocytosis. The complex can associate physically with hyperphosphorylated RNA polymerase II; it contains two discrete heterotrimeric subcomplexes. |
| elongin complex | A transcription elongation factor complex that suppresses RNA polymerase II pausing, and may act by promoting proper alignment of the 3'-end of nascent transcripts with the polymerase catalytic site. Consists of a transcriptionally active Elongin A subunit (abut 100 kDa)and two smaller Elongin B (about 18 kDa) and Elongin C (about 15 kDa)subunits. |
| endocytic vesicle | A membrane-bounded intracellular vesicle formed by invagination of the plasma membrane around an extracellular substance. Endocytic vesicles fuse with early endosomes to deliver the cargo for further sorting. |
| endocytic vesicle lumen | The volume enclosed by the membrane of an endocytic vesicle. |
| endocytic vesicle membrane | The lipid bilayer surrounding an endocytic vesicle. |
| endolysosome | An transient hybrid organelle formed by fusion of a late endosome with a lysosome, and in which active degradation takes place. |
| endolysosome lumen | The volume enclosed by the membrane of an endolysosome. An endolysosome is a transient hybrid organelle formed by fusion of a late endosome with a lysosome. |
| endolysosome membrane | The lipid bilayer surrounding an endolysosome. An endolysosome is a transient hybrid organelle formed by fusion of a late endosome with a lysosome. |
| endomembrane system | A collection of membranous structures involved in transport within the cell. The main components of the endomembrane system are endoplasmic reticulum, Golgi bodies, vesicles, cell membrane and nuclear envelope. Members of the endomembrane system pass materials through each other or though the use of vesicles. |
| endopeptidase clp complex | A protein complex comprised of members of the ClpX, ClpC, ClpD, ClpP or ClpR protein families. ClpPs are the proteolytic subunit of active complexes, and ClpA and ClpX form the regulatory subunits. Enzymatically active and inactive complexes can form. |
| endoplasmic reticulum | The irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached). |
| endoplasmic reticulum chaperone complex | A protein complex that is located in the endoplasmic reticulum and is composed of chaperone proteins, including BiP, GRP94; CaBP1, protein disulfide isomerase (PDI), ERdj3, cyclophilin B, ERp72, GRP170, UDP-glucosyltransferase, and SDF2-L1. |
| endoplasmic reticulum exit site | An endoplasmic reticulum part at which COPII-coated vesicles are produced. |
| endoplasmic reticulum lumen | The volume enclosed by the membranes of the endoplasmic reticulum. |
| endoplasmic reticulum membrane | The lipid bilayer surrounding the endoplasmic reticulum. |
| endoplasmic reticulum palmitoyltransferase complex | A dimeric complex of the endoplasmic reticulum that catalyzes S-palmitoylation, the addition of palmitate (C16:0) or other long-chain fatty acids to proteins at a cysteine residue. |
| endoplasmic reticulum part | Any constituent part of the endoplasmic reticulum, the irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells. The membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. |
| endoplasmic reticulum quality control compartment | A subcompartment of the endoplasmic reticulum in which proteins with improper or incorrect folding accumulate. Enzymes in this compartment direct proteins with major folding problems to translocation to the cytosol and degradation, and proteins with minor folding problems to the ER, to interact with chaperon proteins. |
| endoplasmic reticulum sec complex | An endoplasmic reticulum membrane-associated complex involved in the translocation of proteins that are targeted to the ER. In yeast, this complex consists of two subcomplexes, namely, the Sec61 complex and the Sec62/Sec63 complex. |
| endoplasmic reticulum tubular network | An endoplasmic reticulum part that comprises the membranes with high curvature in cross-section. |
| endoplasmic reticulum-golgi intermediate compartment | A complex system of membrane-bounded compartments located between endoplasmic reticulum (ER) and the Golgi complex, with a distinctive membrane protein composition; involved in ER-to-Golgi transport. |
| endoplasmic reticulum-golgi intermediate compartment membrane | The lipid bilayer surrounding any of the compartments of the endoplasmic reticulum (ER)-Golgi intermediate compartment system. |
| endoribonuclease complex | A protein complex which is capable of endoribonuclease activity. |
| endosomal part | Any constituent part of an endosome, a membrane-bounded organelle to which materials ingested by endocytosis are delivered. |
| endosome | A membrane-bounded organelle to which materials ingested by endocytosis are delivered. |
| endosome lumen | The volume enclosed by the membrane of an endosome. |
| endosome membrane | The lipid bilayer surrounding an endosome. |
| endothelial microparticle | A blood microparticle that is derived from, and contains membrane receptors as well as other proteins characteristic of, an endothelial cell. |
| envelope | A multilayered structure surrounding all or part of a cell; encompasses one or more lipid bilayers, and may include a cell wall layer; also includes the space between layers. |
| epidermal lamellar body | A specialized secretory organelle found in keratinocytes and involved in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function. |
| epsilon dna polymerase complex | A heterotetrameric DNA polymerase complex that catalyzes processive DNA synthesis in the absence of PCNA, but is further stimulated in the presence of PCNA. The complex contains a large catalytic subunit and three small subunits, and is best characterized in Saccharomyces, in which the subunits are named Pol2p, Dpb2p, Dpb3p, and Dpb4p. Some evidence suggests that DNA polymerase epsilon is the leading strand polymerase; it is also involved in nucleotide-excision repair and mismatch repair. |
| er membrane insertion complex | A protein complex that is involved in the post-translational delivery of tail-anchored (TA) membrane proteins to the endoplasmic reticulum. TA membrane proteins, also called type II transmembrane proteins, contain a single C-terminal transmembrane region. Some ER membrane insertion complex subunits are conserved between different species such as mammals and budding yeast. |
| er membrane protein complex | A transmembrane protein complex that is involved in protein folding in the endoplasmic reticulum. In S. cerevisiae, it has six members: EMC1, EMC2, AIM27, EMC4, KRE27, and EMC6. |
| er to golgi transport vesicle | A vesicle that mediates transport from the endoplasmic reticulum to the Golgi complex; bears a coat formed of the COPII coat complex proteins; such vesicles found associated with endoplasmic reticulum (ER) membranes at steady state, and are involved in ER to Golgi (anterograde) vesicle transport. |
| er to golgi transport vesicle membrane | The lipid bilayer surrounding a vesicle transporting substances from the endoplasmic reticulum to the Golgi. |
| er ubiquitin ligase complex | A ubiquitin ligase complex found in the ER. |
| er-mitochondrion membrane contact site | A zone of apposition between endoplasmic-reticulum and mitochondrial membranes, structured by bridging complexes. These contact sites are thought to facilitate inter-organelle calcium and phospholipid exchange. |
| esc/e(z) complex | A multimeric protein complex that can methylate lysine-27 and lysine-9 residues of histone H3. In Drosophila the core subunits of the complex include ESC, E(Z), CAF1 (NURF-55) and SU(Z)12. In mammals the core subunits of the complex include EED, EZH2, SUZ12 and RBBP4. |
| escrt complex | An endosomal sorting complex required for transport. |
| escrt i complex | An endosomal sorting complex required for transport. It consists of the class E vacuolar protein sorting (Vps) proteins and interacts with ubiquitinated cargoes. |
| escrt iii complex | An endosomal sorting complex required for transport. Consists of two soluble subcomplexes of highly charged coiled-coil proteins and is required for sorting and/or concentration of multivesicular body (MVB) cargoes. |
| euchromatin | A dispersed and relatively uncompacted form of chromatin. |
| eukaryotic 43s preinitiation complex | A protein complex composed of the 40S ribosomal subunit plus eIF1A, eIF3, and eIF2-GTP-bound methionyl-initiator methionine tRNA. |
| eukaryotic 48s preinitiation complex | A protein complex composed of the small ribosomal subunit, eIF3, eIF1A, methionyl-initiatior methionine and a capped mRNA. The complex is initially positioned at the 5'-end of the capped mRNA. |
| eukaryotic 80s initiation complex | A protein complex composed of the large and small ribosomal subunits, methionyl-initiatior tRNA, and the capped mRNA. The initiator tRNA is positioned at the ribosomal P site at the AUG codon corresponding to the beginning of the coding region. |
| eukaryotic translation elongation factor 1 complex | A multisubunit nucleotide exchange complex that binds GTP and aminoacyl-tRNAs, and catalyzes their codon-dependent placement at the A-site of the ribosome. In humans, the complex is composed of four subunits, alpha, beta, delta and gamma. |
| eukaryotic translation initiation factor 2 complex | Complex of three heterogeneous polypeptide chains, that form a ternary complex with initiator methionyl-tRNA and GTP. This ternary complex binds to free 40S subunit, which subsequently binds the 5' end of mRNA. |
| eukaryotic translation initiation factor 2b complex | A multisubunit guanine nucleotide exchange factor which catalyzes the exchange of GDP bound to initiation factor eIF2 for GTP, generating active eIF2-GTP. In humans, it is composed of five subunits, alpha, beta, delta, gamma and epsilon. |
| eukaryotic translation initiation factor 3 complex | A complex of several polypeptides that plays at least two important roles in protein synthesis: First, eIF3 binds to the 40S ribosome and facilitates loading of the Met-tRNA/eIF2.GTP ternary complex to form the 43S preinitiation complex. Subsequently, eIF3 apparently assists eIF4 in recruiting mRNAs to the 43S complex. The eIF3 complex contains five conserved core subunits, and may contain several additional proteins; the non-core subunits are thought to mediate association of the complex with specific sets of mRNAs. |
| eukaryotic translation initiation factor 3 complex, eif3m | An eukaryotic translation initiation factor 3 complex that contains the PCI-domain protein eIF3m. |
| eukaryotic translation initiation factor 4f complex | The eukaryotic translation initiation factor 4F complex is composed of eIF4E, eIF4A and eIF4G; it is involved in the recognition of the mRNA cap, ATP-dependent unwinding of the 5'-terminal secondary structure and recruitment of the mRNA to the ribosome. |
| excitatory synapse | A synapse in which an action potential in the presynaptic cell increases the probability of an action potential occurring in the postsynaptic cell. |
| exocyst | A protein complex peripherally associated with the plasma membrane that determines where vesicles dock and fuse. At least eight complex components are conserved between yeast and mammals. |
| exocytic vesicle | A transport vesicle that mediates transport from an intracellular compartment to the plasma membrane, and fuses with the plasma membrane to release various cargo molecules, such as proteins or hormones, by exocytosis. |
| exon-exon junction complex | A multi-subunit complex deposited by the spliceosome upstream of messenger RNA exon-exon junctions. The exon-exon junction complex provides a binding platform for factors involved in mRNA export and nonsense-mediated mRNA decay. |
| exosome (rnase complex) | Complex of 3'-5' exoribonucleases. |
| external encapsulating structure | A structure that lies outside the plasma membrane and surrounds the entire cell. |
| external encapsulating structure part | Any constituent part of an external encapsulating structure, a structure that lies outside the plasma membrane and surrounds the entire cell. |
| external side of cell outer membrane | The side of the outer membrane that is opposite to the side that faces the periplasm of the cell. |
| external side of plasma membrane | The leaflet of the plasma membrane that faces away from the cytoplasm and any proteins embedded or anchored in it or attached to its surface. |
| extracellular matrix | A structure lying external to one or more cells, which provides structural support for cells or tissues; may be completely external to the cell (as in animals and bacteria) or be part of the cell (as in plants). |
| extracellular matrix part | Any constituent part of the extracellular matrix, the structure lying external to one or more cells, which provides structural support for cells or tissues; may be completely external to the cell (as in animals) or be part of the cell (as often seen in plants). |
| extracellular membrane-bounded organelle | Organized structure of distinctive morphology and function, bounded by a lipid bilayer membrane and occurring outside the cell. |
| extracellular organelle | Organized structure of distinctive morphology and function, occurring outside the cell. Includes, for example, extracellular membrane vesicles (EMVs) and the cellulosomes of anaerobic bacteria and fungi. |
| extracellular region | The space external to the outermost structure of a cell. For cells without external protective or external encapsulating structures this refers to space outside of the plasma membrane. This term covers the host cell environment outside an intracellular parasite. |
| extracellular region part | Any constituent part of the extracellular region, the space external to the outermost structure of a cell. For cells without external protective or external encapsulating structures this refers to space outside of the plasma membrane. This term covers constituent parts of the host cell environment outside an intracellular parasite. |
| extracellular space | That part of a multicellular organism outside the cells proper, usually taken to be outside the plasma membranes, and occupied by fluid. |
| extracellular vesicle | Any vesicle that is part of the extracellular region. |
| extracellular vesicular exosome | A membrane-bounded vesicle that is released into the extracellular region by fusion of the limiting endosomal membrane of a multivesicular body with the plasma membrane. |
| extraorganismal space | The environmental space outside of an organism; this may be a host organism in the case of parasitic and symbiotic organisms. |
| extrinsic component of cytoplasmic side of plasma membrane | The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to its cytoplasmic surface, but not integrated into the hydrophobic region. |
| extrinsic component of endoplasmic reticulum membrane | The component of the endoplasmic reticulum membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of endosome membrane | The component of an endosome membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of external side of plasma membrane | The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to its external surface, but not integrated into the hydrophobic region. |
| extrinsic component of golgi membrane | The component of a Golgi membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of membrane | The component of a membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of mitochondrial inner membrane | The component of mitochondrial inner membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of mitochondrial outer membrane | The component of a mitochondrial outer membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of organelle membrane | The component of an organelle membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| extrinsic component of plasma membrane | The component of a plasma membrane consisting of gene products and protein complexes that are loosely bound to one of its surfaces, but not integrated into the hydrophobic region. |
| f-actin capping protein complex | A heterodimer consisting of alpha and beta subunits that binds to and caps the barbed ends of actin filaments, thereby regulating the polymerization of actin monomers but not severing actin filaments. |
| facit collagen trimer | A collagen trimer that associates with collagen fibrils and consists of collagen monomers that contain two or more relatively short triple-helical domains connected by non-triple-helical sequences. |
| fancm-mhf complex | A protein complex contains the proteins FANCM and MHF, or their orthologs, plays an essential role in DNA remodeling, protects replication forks, and is conserved in eukaryotes. |
| fanconi anaemia nuclear complex | A protein complex composed of the Fanconi anaemia (FA) proteins including A, C, E, G and F (FANCA-F). Functions in the activation of the downstream protein FANCD2 by monoubiquitylation, and is essential for protection against chromosome breakage. |
| fascia adherens | A cell-cell adherens junction that contains the transmembrane protein N-cadherin, which interacts with identical molecules from neighboring cells to form a tight mechanical intercellular link; forms a large portion of the intercalated disc, the structure at which myofibrils terminate in cardiomyocytes. |
| fatty acid beta-oxidation multienzyme complex | A multienzyme complex possessing three kinds of enzymes that catalyze the chain reactions in the fatty acid beta-oxidation cycle, enoyl-CoA hydratase (ECH), 3-hydroxyacyl-CoA dehydrogenase (HACD), and acetyl-CoA C-acyltransferase (KACT). |
| fc receptor complex | A protein complex composed of a subunit or subunits capable of binding the Fc portion of an immunoglobulin with additional signaling components. The complex functions as a receptor for immunoglobulin. |
| fc-epsilon receptor i complex | A protein complex composed of an Fc-epsilon RI alpha chain and an Fc-epsilon RI gamma chain dimer with or without an Fc-episilon RI beta chain and additional signaling components. The complex functions primarily as an activating receptor for IgE. |
| female germ cell nucleus | The nucleus of the female germ cell, a reproductive cell in females. |
| female pronucleus | The pronucleus originating from the ovum that is being fertilized. |
| ferritin complex | A protein complex that binds iron and acts as a major iron storage system. Intracellular and extracellular ferritin complexes have different ratios of two types of ferritin monomer, the L (light) chain and H (heavy) chain. |
| fhf complex | A protein complex that is composed of AKTIP/FTS, FAM160A2/p107FHIP, and one or more members of the Hook family of proteins, HOOK1, HOOK2, and HOOK3. The complex is thought to promote vesicle trafficking and/or fusion, and associates with the homotypic vesicular sorting complex (the HOPS complex). |
| fibril | Extracellular matrix material consisting of polysaccharides and protein. |
| fibrillar center | A structure found most metazoan nucleoli, but not usually found in lower eukaryotes; surrounded by the dense fibrillar component; the zone of transcription from multiple copies of the pre-rRNA genes is in the border region between these two structures. |
| fibrillar collagen trimer | Any triple helical collagen trimer that forms fibrils. |
| fibrinogen complex | A highly soluble, elongated protein complex found in blood plasma and involved in clot formation. It is converted into fibrin monomer by the action of thrombin. In the mouse, fibrinogen is a hexamer, 46 nm long and 9 nm maximal diameter, containing two sets of nonidentical chains (alpha, beta, and gamma) linked together by disulfide bonds. |
| filamentous actin | A two-stranded helical polymer of the protein actin. |
| filopodium | Thin, stiff protrusion extended by the leading edge of a motile cell such as a crawling fibroblast or amoeba, or an axonal or dendritic growth cone, or a dendritic shaft. |
| filopodium membrane | The portion of the plasma membrane surrounding a filopodium. |
| filopodium tip | The end of a filopodium distal to the body of the cell. |
| filtration diaphragm | A specialized cell-cell junction found between the cells of the excretory system, which provides a barrier for filtration of blood or hemolymph. |
| flemming body | A cell part that is the central region of the midbody characterized by a gap in alpha-tubulin staining. It is a dense structure of antiparallel microtubules from the central spindle in the middle of the intercellular bridge. |
| flotillin complex | A protein complex that contains flotillin-1 and flotillin-2, and may contain associated proteins. Flotillins associate into membrane microdomains resembling caveolae. |
| focal adhesion | Small region on the surface of a cell that anchors the cell to the extracellular matrix and that forms a point of termination of actin filaments. |
| fumarate reductase complex | A membrane-bound flavoenzyme complex consisting of four subunits, A, B, C, and D. A and B comprise the membrane-extrinsic catalytic domain and C (InterPro:IPR003510; InterPro:IPR004224) and D (InterPro:IPR003418) link the catalytic centers to the electron-transport chain. This family consists of the 13 kDa hydrophobic subunit D. This component may be required to anchor the catalytic components of the fumarate reductase complex to the cytoplasmic membrane. Fumarate reductase couples the reduction of fumarate to succinate to the oxidation of quinol to quinone, in a reaction opposite to that catalyzed by the related complex II of the respiratory chain (succinate dehydrogenase-(ubiquinone)). |
| g-protein coupled receptor complex | A protein complex that contains G-protein coupled receptors. |
| g-protein coupled receptor dimeric complex | A protein complex that contains two G-protein coupled receptors. |
| g-protein coupled receptor heterodimeric complex | A protein complex that contains two G-protein coupled receptors (GPCRs) of different subtypes. Formation of a GPCR heterodimer may alter the functional property of the GPCR. |
| g-protein coupled receptor homodimeric complex | A protein complex that contains two G-protein coupled receptors (GPCRs) of the same subtype. Formation of a GPCR homodimer may be important for the transport of newly formed receptors to the cell surface, and the function of the receptor. |
| gait complex | A protein complex which mediates interferon-gamma-induced transcript-selective translation inhibition in inflammation processes. The complex binds to stem loop-containing GAIT elements in the 3'-UTR of diverse inflammatory mRNAs and suppresses their translation by blocking the recruitment of the 43S ribosomal complex to m7G cap-bound eIF4G. In humans it includes RPL13A, EPRS, SYNCRIP and GAPDH; mouse complexes lack SYNCRIP. |
| gamma dna polymerase complex | A DNA polymerase complex consisting of a large subunit, responsible for the catalytic activities, and a small accessory subunit. Functions in the replication and repair of mitochondrial DNA. |
| gamma-catenin-tcf7l2 complex | A protein complex that contains gamma-catenin and TCF7L2 (TCF4), binds to the TCF DNA motif within a promoter element, and is involved in the regulation of WNT target gene transcription. |
| gamma-secretase complex | A protein complex that has aspartic-type endopeptidase activity, and contains a catalytic subunit, presenilin (PS), that is a prototypical member of the GxGD-type aspartyl peptidases. The complex also contains additional subunits, including nicastrin, APH-1, PEN-2, and a regulatory subunit, CD147. Gamma-secretase cleaves several transmembrane proteins including the cell surface receptor Notch and the beta-amyloid precursor protein. |
| gamma-tubulin complex | A multiprotein complex composed of gamma-tubulin and other non-tubulin proteins. Gamma-tubulin complexes are localized to microtubule organizing centers, and play an important role in the nucleation of microtubules. The number and complexity of non-tubulin proteins associated with these complexes varies between species. |
| gamma-tubulin large complex | A complex of gamma tubulin and associated proteins thought to be formed by multimerization of gamma-tubulin small complexes. An example of this structure is found in Schizosaccharomyces pombe. |
| gamma-tubulin ring complex | A multiprotein complex composed of gamma-tubulin and other non-tubulin proteins that forms a flexible open ring structure thought to be the unit of nucleation at the minus end of a microtubule. |
| gamma-tubulin small complex | A complex usually comprising two gamma-tubulin molecules and two conserved non-tubulin proteins. Some gamma-tubulin small complexes are thought to be the repeating unit making up the core of the gamma-tubulin ring complex. |
| gap junction | A cell-cell junction that is composed of an array of small channels that permit small molecules to pass from one cell to another. At gap junctions, the membranes of two adjacent cells are separated by a uniform narrow gap of about 2-4 nm that is spanned by channel-forming proteins called connexins, which form hexagonal tubes called connexons. |
| garp complex | A quatrefoil tethering complex required for retrograde traffic from the early endosome back to the late Golgi and biogenesis of cytoplasmic vesicles. |
| germ cell nucleus | The nucleus of a germ cell, a reproductive cell in multicellular organisms. |
| germ plasm | Differentiated cytoplasm associated with a pole of an oocyte, egg or early embryo that will be inherited by the cells that will give rise to the germ line. |
| germinal vesicle | The enlarged, fluid filled nucleus of a primary oocyte, the development of which is suspended in prophase I of the first meiotic division between embryohood and sexual maturity. |
| glial cell projection | A prolongation or process extending from a glial cell. |
| glial limiting end-foot | Terminal process of astrocyte that extends to the surface of the central nervous system. Together, glial limiting end-feet form the glial limiting membrane or glia limitans. |
| glomerular endothelium fenestra | A large plasma membrane-lined circular pore that perforates the flattened glomerular endothelium and, unlike those of other fenestrated capillaries, is not spanned by diaphragms; the density and size of glomerular fenestrae account, at least in part, for the high permeability of the glomerular capillary wall to water and small solutes. |
| glucosidase ii complex | A heterodimeric complex that catalyzes the trimming of glucose residues from N-linked core glycans on newly synthesized glycoproteins. |
| glutamate-cysteine ligase complex | An enzyme complex that catalyzes the ligation of glutamate to cysteine, forming glutamylcysteine. |
| glutamyl-trna(gln) amidotransferase complex | A protein complex that possesses glutamyl-tRNA(Gln) amidotransferase activity, and therefore creates Gln-tRNA by amidating Glu-tRNA; usually composed of 3 subunits: A, B, and C. Note that the C subunit may not be required in all organisms. |
| glycerol-3-phosphate dehydrogenase complex | An enzyme complex that catalyzes the dehydrogenation of sn-glycerol 3-phosphate to form glycerone phosphate. |
| glycine cleavage complex | A protein complex that catalyzes the reversible oxidation of glycine. In E. coli, it has four components: dihydrolipoamide dehydrogenase, glycine dehydrogenase (decarboxylating), lipoyl-GcvH-protein and aminomethyltransferase, also known as L, P, H, and T. |
| glycocalyx | A viscous, carbohydrate rich layer at the outermost periphery of a cell. |
| glycogen granule | Cytoplasmic bead-like structures of animal cells, visible by electron microscope. Each granule is a functional unit with the biosynthesis and catabolism of glycogen being catalyzed by enzymes bound to the granule surface. |
| glycosylphosphatidylinositol-n-acetylglucosaminyltransferase (gpi-gnt) complex | An enzyme complex that catalyzes the transfer of GlcNAc from UDP-GlcNAc to an acceptor phosphatidylinositol, the first step in the production of GPI anchors for cell surface proteins. The complex contains PIG-A, PIG-C, PIG-H, PIG-Q, PIG-P, and DPM2 in human, and Eri1p, Gpi1p, Gpi2p, Gpi15p, Gpi19p, and Spt14p in budding yeast. |
| golgi apparatus | A compound membranous cytoplasmic organelle of eukaryotic cells, consisting of flattened, ribosome-free vesicles arranged in a more or less regular stack. The Golgi apparatus differs from the endoplasmic reticulum in often having slightly thicker membranes, appearing in sections as a characteristic shallow semicircle so that the convex side (cis or entry face) abuts the endoplasmic reticulum, secretory vesicles emerging from the concave side (trans or exit face). In vertebrate cells there is usually one such organelle, while in invertebrates and plants, where they are known usually as dictyosomes, there may be several scattered in the cytoplasm. The Golgi apparatus processes proteins produced on the ribosomes of the rough endoplasmic reticulum; such processing includes modification of the core oligosaccharides of glycoproteins, and the sorting and packaging of proteins for transport to a variety of cellular locations. Three different regions of the Golgi are now recognized both in terms of structure and function: cis, in the vicinity of the cis face, trans, in the vicinity of the trans face, and medial, lying between the cis and trans regions. |
| golgi apparatus part | Any constituent part of the Golgi apparatus, a compound membranous cytoplasmic organelle of eukaryotic cells, consisting of flattened, ribosome-free vesicles arranged in a more or less regular stack. |
| golgi cis cisterna | The Golgi cisterna closest to the endoplasmic reticulum; the first processing compartment through which proteins pass after export from the ER. |
| golgi cisterna | Any of the thin, flattened membrane-bounded compartments that form the central portion of the Golgi complex. |
| golgi cisterna membrane | The lipid bilayer surrounding any of the thin, flattened compartments that form the central portion of the Golgi complex. |
| golgi lumen | The volume enclosed by the membranes of any cisterna or subcompartment of the Golgi apparatus, including the cis- and trans-Golgi networks. |
| golgi medial cisterna | The middle Golgi cisterna (or cisternae). |
| golgi membrane | The lipid bilayer surrounding any of the compartments of the Golgi apparatus. |
| golgi stack | The set of thin, flattened membrane-bounded compartments, called cisternae, that form the central portion of the Golgi complex. The stack usually comprises cis, medial, and trans cisternae; the cis- and trans-Golgi networks are not considered part of the stack. |
| golgi trans cisterna | The Golgi cisterna farthest from the endoplasmic reticulum; the final processing compartment through which proteins pass before exiting the Golgi apparatus; the compartment in which N-linked protein glycosylation is completed. |
| golgi transport complex | A complex of proteins that, in vitro, stimulates intra-Golgi transport; a 13S complex, about 800 kDa in size and consists of at least five polypeptides. In yeast, this complex is called the Sec34/35 complex and is composed of eight subunits (Sec34p, Sec35p, Dor1p, Cod1p, Cod2p, Cod3p, Cod4p, and Cod5p). |
| golgi-associated vesicle | Any vesicle associated with the Golgi complex and involved in mediating transport within the Golgi or between the Golgi and other parts of the cell. |
| golgi-associated vesicle membrane | The lipid bilayer surrounding a vesicle associated with the Golgi apparatus. |
| gpi-anchor transamidase complex | An enzyme complex which in humans and yeast consists of at least five proteins; for example, the complex contains GAA1, GPI8, PIG-S, PIG-U, and PIG-T in human, and Gaa1p, Gab1p, Gpi8p, Gpi16p, and Gpi17p in yeast. Catalyzes the posttranslational attachment of the carboxyl-terminus of a precursor protein to a GPI-anchor. |
| granular component | A structure found in the nucleolus, which contains nearly completed preribosomal particles destined for the cytoplasm. |
| granulocyte macrophage colony-stimulating factor receptor complex | The heterodimeric receptor for granulocyte macrophage colony-stimulating factor. |
| grb2-egfr complex | A protein complex that contains the epidermal growth factor receptor (EGFR) and Grb2, and is involved in linking EGFR activation to the p21-Ras pathway. |
| grb2-sos complex | A protein complex that contains Grb2 and the guanine nucleotide exchange factor Sos (or an ortholog thereof, such as mSos1), and is involved in linking EGFR activation to the p21-Ras pathway. |
| growing cell tip | The region at either end of the longest axis of a cylindrical or elongated cell, where polarized growth occurs. |
| growth cone | The migrating motile tip of a growing nerve cell axon or dendrite. |
| growth cone membrane | The portion of the plasma membrane surrounding a growth cone. |
| growth factor complex | A protein complex that has growth factor activity. |
| growth hormone receptor complex | A receptor complex that consists of two identical subunits and binds growth hormone. |
| guanyl-nucleotide exchange factor complex | A protein complex that stimulates the exchange of guanyl nucleotides associated with a GTPase. |
| guanylate cyclase complex, soluble | Complex that possesses guanylate cyclase activity and is not bound to a membrane. |
| h zone | A relatively pale zone traversing the center of the A band of a sarcomere, visible in relaxed muscle fibers; consists of the central portion of thick (myosin) filaments that are not overlapped by thin (actin) filaments. |
| h3 histone acetyltransferase complex | A multisubunit complex that catalyzes the acetylation of histone H3. |
| h4 histone acetyltransferase complex | A protein complex which is capable of H4 histone acetyltransferase activity. |
| h4/h2a histone acetyltransferase complex | A multisubunit complex that catalyzes the acetylation of histones H4 and H2A. |
| haptoglobin-hemoglobin complex | A protein complex formed by the stable binding of a haptoglobin to hemoglobin. |
| haus complex | A protein complex that localizes to interphase centrosomes and to mitotic spindle tubules and regulates mitotic spindle assembly and centrosome integrity; in human, the complex consists of eight subunits, some of which are homologous to subunits of the Drosophila Augmin complex. |
| hemidesmosome | A cell-substrate junction that forms a point of contact between the basal surface of epithelial cells and the basal lamina. Morphologically resembles desmosomes; attached to intermediate filaments. |
| hemoglobin complex | An iron-containing, oxygen carrying complex. In vertebrates it is made up of two pairs of associated globin polypeptide chains, each chain carrying a noncovalently bound heme prosthetic group. |
| heterochromatin | A compact and highly condensed form of chromatin. |
| heterotrimeric g-protein complex | Any of a family of heterotrimeric GTP-binding and hydrolyzing proteins; they belong to a superfamily of GTPases that includes monomeric proteins such as EF-Tu and RAS. Heterotrimeric G-proteins consist of three subunits; the alpha subunit contains the guanine nucleotide binding site and possesses GTPase activity; the beta and gamma subunits are tightly associated and function as a beta-gamma heterodimer; extrinsic plasma membrane proteins (cytoplasmic face) that function as a complex to transduce signals from G-protein coupled receptors to an effector protein. |
| hexameric igm immunoglobulin complex | A circulating form of IgM consisting of a hexamer of IgM core units with a single J chain polypeptide. |
| high-density lipoprotein particle | A lipoprotein particle with a high density (typically 1.063-1.21 g/ml) and a diameter of 5-10 nm that contains APOAs and may contain APOCs and APOE; found in blood and carries lipids from body tissues to the liver as part of the reverse cholesterol transport process. |
| histone acetyltransferase complex | A protein complex that possesses histone acetyltransferase activity. |
| histone deacetylase complex | A protein complex that possesses histone deacetylase activity. |
| histone locus body | A nuclear body associated with the histone gene locus that is thought to contain all of the factors necessary for histone mRNA transcription and pre-mRNA processing. In Drosophila, U7 snRNP is located in the histone locus body rather than the distinct Cajal body. |
| histone methyltransferase complex | A multimeric complex that is able to catalyze the addition of methyl groups to histone proteins. |
| histone pre-mrna 3'end processing complex | A ribonucleoprotein that binds to specific sites in, and is required for cleavage of, the 3'-end of histone pre-mRNAs. The complex contains the U7 snRNP and additional proteins, including the stem-loop binding protein (SLBP) and the exonuclease 3'hExo/Eri-1. |
| holo tfiih complex | A complex that is capable of kinase activity directed towards the C-terminal Domain (CTD) of the largest subunit of RNA polymerase II and is essential for initiation at RNA polymerase II promoters in vitro. It is composed of the core TFIIH complex and the TFIIK complex. |
| hops complex | A multimeric protein complex that associates with the vacuolar membrane, late endosomal (multivesicular body) and lysosomal membranes. HOPS is a tethering complex involved in vesicle fusion. |
| host | Any organism in which another organism, especially a parasite or symbiont, spends part or all of its life cycle and from which it obtains nourishment and/or protection. |
| host cell | A cell within a host organism. Includes the host plasma membrane and any external encapsulating structures such as the host cell wall and cell envelope. |
| host cell cytoplasm | The cytoplasm of a host cell. |
| host cell cytoplasm part | Any constituent part of the host cell cytoplasm, all of the contents of a cell excluding the plasma membrane and nucleus, but including other subcellular structures. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host cell membrane | Double layer of lipid molecules as it encloses host cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host cell nucleus | A membrane-bounded organelle as it is found in the host cell in which chromosomes are housed and replicated. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host cell part | Any constituent part of a host cell. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host cell presynaptic membrane | A specialized area of membrane of the host axon terminal that faces the plasma membrane of the host neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many host synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane. |
| host cell synapse | The junction between a nerve fiber of one host neuron and another host neuron or muscle fiber or glial cell; the site of interneuronal communication. |
| host cell viral assembly compartment | A membrane-bounded compartment that forms in the cytoplasm of the host cell, in which virus assembly takes place. |
| host intracellular membrane-bounded organelle | Organized structure of distinctive morphology and function, as found in host cells, bounded by a single or double lipid bilayer membrane and occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host intracellular organelle | Organized structure of distinctive morphology and function, occurring within the host cell. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton. Excludes the plasma membrane. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| host intracellular part | Any constituent part of the living contents of a host cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm. The host is defined as the larger of the organisms involved in a symbiotic interaction. |
| hrd1p ubiquitin ligase complex | A multiprotein complex that recognizes and ubiquitinates proteins with misfolded luminal and membrane domains during ER-associated protein degradation (ERAD). In S. cerevisiae, this complex contains the ubiquitin ligase Hrd1p. |
| hulc complex | A ubiquitin-conjugating enzyme complex that contains two RING finger proteins, which have ubiquitin ligase activity, in addition to a protein with ubiquitin-conjugating enzyme activity; catalyzes the ubiquitination of histone H2B at lysine 119 (or the equivalent residue). In Schizosaccharomyces the subunits are Rhp1, Brl2/Rfp1 and Brl1/Rfp2. |
| hyaluranon cable | A cable structure, surrounding some cell types (e.g. proximal or bronchial tubular epithelial cells), and composed of hyaluranon (HA), a ubiquitous connective tissue glycosaminoglycan. |
| hydrogen:potassium-exchanging atpase complex | A protein complex that possesses hydrogen:potassium-exchanging ATPase activity; characterized in animal cells, where it maintains ionic gradients of K+ at the expense of ATP hydrolysis; The complex contains two obligatory subunits, the catalytic alpha subunit and a glycosylated beta subunit; two additional subunits, gamma and channel-inducing factor (CHIF), may also be present. |
| i band | A region of a sarcomere that appears as a light band on each side of the Z disc, comprising a region of the sarcomere where thin (actin) filaments are not overlapped by thick (myosin) filaments; contains actin, troponin, and tropomyosin; each sarcomere includes half of an I band at each end. |
| i-kappab/nf-kappab complex | A protein complex containing an inhibitory-kappaB (I-kappaB/IKB) protein and one or more copies of an NF-kappaB protein. In the resting state, NF-kappaB dimers are bound to I-kappaB proteins, sequestering NF-kappaB in the cytoplasm. |
| iga immunoglobulin complex | A protein complex composed of two identical immunoglobulin heavy chains of the IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and sometimes complexed with J chain or J chain and secretory component. An IgA immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| iga immunoglobulin complex, circulating | A protein complex composed of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, sometimes complexed with J chain or J chain and secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| igm immunoglobulin complex | A protein complex composed of two identical immunoglobulin heavy chains of the IgM isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and in its circulating form complexed with J chain in polymeric forms. An IgM immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| igm immunoglobulin complex, circulating | A polymer of five or six IgM core units each composed of two identical immunoglobulin heavy chains of the IgM isotype and two identical immunoglobulin light chains, held together by disulfide bonds; the individual IgM core units are held together via disulfide bonds with a single J chain polypeptide acting as a bridge between two of the polymeric units. Circulating IgM is present in the extracellular space, in mucosal areas or other tissues, or in the blood or lymph. |
| ikappab kinase complex | A trimeric protein complex that phosphorylates inhibitory-kappaB (I-kappaB) proteins. The complex is composed of two kinase subunits (alpha and beta) and a regulatory gamma subunit (also called NEMO). In a resting state, NF-kappaB dimers are bound to inhibitory IKB proteins, sequestering NF-kappaB in the cytoplasm. Phosphorylation of I-kappaB targets I-kappaB for ubiquitination and proteasomal degradation, thus releasing the NF-kappaB dimers, which can translocate to the nucleus to bind DNA and regulate transcription. |
| immunoglobulin complex | A protein complex that in its canonical form is composed of two identical immunoglobulin heavy chains and two identical immunoglobulin light chains, held together by disulfide bonds and sometimes complexed with additional proteins. An immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| immunoglobulin complex, circulating | An immunoglobulin complex that is secreted into extracellular space and found in mucosal areas or other tissues or circulating in the blood or lymph. In its canonical form, a circulating immunoglobulin complex is composed of two identical heavy chains and two identical light chains, held together by disulfide bonds. Some forms of are polymers of the basic structure and contain additional components such as J-chain and the secretory component. |
| immunological synapse | An area of close contact between a lymphocyte (T-, B-, or natural killer cell) and a target cell formed through the clustering of particular signaling and adhesion molecules and their associated membrane rafts on both the lymphocyte and the target cell and facilitating activation of the lymphocyte, transfer of membrane from the target cell to the lymphocyte, and in some situations killing of the target cell through release of secretory granules and/or death-pathway ligand-receptor interaction. |
| inclusion body | A discrete intracellular part formed of aggregated molecules such as proteins or other biopolymers. |
| inhibin a complex | Heterodimeric hormone composed of an inhibin alpha subunit complexed with an inhibin beta-A subunit. |
| inhibin complex | Heterodimeric hormone composed of an inhibin alpha subunit complexed with either an inhibin beta-A subunit, to form inhibin A, or an inhibin beta-B subunit, to form inhibin B. |
| inhibin-betaglycan-actrii complex | A protein complex that consists of inhibin, type III transforming growth factor beta receptor (also known as betaglycan), and the type II activin receptor ActRII. The complex is thought to negatively regulate the activity of activin B. |
| inhibitory synapse | A synapse in which an action potential in the presynaptic cell reduces the probability of an action potential occurring in the postsynaptic cell. |
| inner acrosomal membrane | The acrosomal membrane region that underlies the acrosomal vesicle and is located toward the sperm nucleus. This region is responsible for molecular interactions allowing the sperm to penetrate the zona pellucida and fuses with the egg plasma membrane. |
| inner mucus layer | The inner of two mucus layers secreted by epithelial cells in the colon; the inner mucus layer is firmly attached to the epithelium, is densely packed with a compact stratified appearance and is devoid of bacteria. |
| ino80 complex | A multisubunit protein complex that contains the Ino80p ATPase; exhibits chromatin remodeling activity and 3' to 5' DNA helicase activity. |
| ino80-type complex | A chromatin remodeling protein complex initially purified from S. cerevisiae and containing more than 10 subunits, including the SWR1-related complexes. INO80 (inositol requiring 80)-type complexes have diverse functions, including promoting transcriptional activation and DNA repair. |
| insulin receptor complex | A disulfide-bonded, heterotetrameric receptor complex. The alpha chains are entirely extracellular, while each beta chain has one transmembrane domain. The ligand binds to the alpha subunit extracellular domain and the kinase is associated with the beta subunit intracellular domain. |
| insulin-like growth factor binding protein complex | A complex of proteins which includes the insulin-like growth factor (IGF) and a number of IGF-binding proteins. The complex plays a role in growth and development. |
| insulin-responsive compartment | A small membrane-bounded vesicle that releases its contents by exocytosis in response to insulin stimulation; the contents are enriched in GLUT4, IRAP and VAMP2. |
| integral component of cell outer membrane | The component of the cell outer membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of cytoplasmic side of endoplasmic reticulum membrane | The component of the endoplasmic reticulum membrane consisting of the gene products that penetrate only the cytoplasmic side of the membrane. |
| integral component of endoplasmic reticulum membrane | The component of the endoplasmic reticulum membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of external side of plasma membrane | The component of the plasma membrane consisting of the gene products that penetrate only the external side of the membrane. |
| integral component of golgi membrane | The component of the Golgi membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of lumenal side of endoplasmic reticulum membrane | The component of the endoplasmic reticulum membrane consisting of the gene products that penetrate only the lumenal side of the membrane. |
| integral component of membrane | The component of a membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of mitochondrial inner membrane | The component of the mitochondrial inner membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of mitochondrial membrane | The component of the mitochondrial membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of mitochondrial outer membrane | The component of the mitochondrial outer membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of nuclear inner membrane | The component of the nuclear inner membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of nuclear outer membrane | The component of the nuclear outer membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of organelle membrane | The component of the organelle membrane consisting of the gene products that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of peroxisomal membrane | The component of the peroxisomal membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of plasma membrane | The component of the plasma membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integral component of synaptic vesicle membrane | The component of the synaptic vesicle membrane consisting of gene products and protein complexes that have some part that penetrates at least one leaflet of the membrane bilayer. This component includes gene products that are buried in the bilayer with no exposure outside the bilayer. |
| integrator complex | A protein complex that stably associates with the C-terminus of RNA polymerase II and mediates 3'-end processing of small nuclear RNAs generated by RNA polymerase II. |
| integrin alpha1-beta1 complex | An integrin complex that comprises one alpha1 subunit and one beta1 subunit. |
| integrin alpha10-beta1 complex | An integrin complex that comprises one alpha10 subunit and one beta1 subunit. |
| integrin alpha11-beta1 complex | An integrin complex that comprises one alpha11 subunit and one beta1 subunit. |
| integrin alpha2-beta1 complex | An integrin complex that comprises one alpha2 subunit and one beta1 subunit. |
| integrin alpha3-beta1 complex | An integrin complex that comprises one alpha3 subunit and one beta1 subunit. |
| integrin alpha4-beta7 complex | An integrin complex that comprises one alpha4 subunit and one beta7 subunit. |
| integrin alpha6-beta4 complex | An integrin complex that comprises one alpha6 subunit and one beta1 subunit. |
| integrin alpha7-beta1 complex | An integrin complex that comprises one alpha7 subunit and one beta1 subunit. |
| integrin alpha8-beta1 complex | An integrin complex that comprises one alpha8 subunit and one beta1 subunit. |
| integrin alpha9-beta1 complex | An integrin complex that comprises one alpha9 subunit and one beta1 subunit. |
| integrin alphaiib-beta3 complex | An integrin complex that comprises one alphaIIb subunit and one beta3 subunit. |
| integrin alphal-beta2 complex | An integrin complex that comprises one alphaL subunit and one beta2 subunit. |
| integrin alphav-beta3 complex | An integrin complex that comprises one alphav subunit and one beta3 subunit. |
| integrin alphav-beta5 complex | An integrin complex that comprises one alphav subunit and one beta5 subunit. |
| integrin alphav-beta8 complex | An integrin complex that comprises one alphav subunit and one beta8 subunit. |
| integrin complex | A protein complex that is composed of one alpha subunit and one beta subunit, both of which are members of the integrin superfamily of cell adhesion receptors; the complex spans the plasma membrane and binds to extracellular matrix ligands, cell-surface ligands, and soluble ligands. |
| intercalated disc | A complex cell-cell junction at which myofibrils terminate in cardiomyocytes; mediates mechanical and electrochemical integration between individual cardiomyocytes. The intercalated disc contains regions of tight mechanical attachment (fasciae adherentes and desmosomes) and electrical coupling (gap junctions) between adjacent cells. |
| intercellular bridge | A direct connection between the cytoplasm of two cells that is formed following the completion of cleavage furrow ingression during cell division. They are usually present only briefly prior to completion of cytokinesis. However, in some cases, such as the bridges between germ cells during their development, they become stabilised. |
| intercellular canaliculus | An extremely narrow tubular channel located between adjacent cells. An instance of this is the secretory canaliculi occurring between adjacent parietal cells in the gastric mucosa of vertebrates. |
| interleukin-1 receptor complex | A protein complex that binds interleukin-1; comprises an alpha and a beta subunit. |
| interleukin-12 complex | A protein complex that is composed of an interleukin-12 alpha (p35, product of the IL12A gene) and an interleukin-12 beta subunit (p40, product of the IL12B gene) and is secreted into the extracellular space. |
| interleukin-12 receptor complex | A protein complex that binds interleukin-12; comprises a beta1 and a beta2 subunit. |
| interleukin-13 receptor complex | A protein complex that binds interleukin-13; consists of two chains, interleukin-13 receptor alpha1 chain and interleukin-4 receptor alpha chain. |
| interleukin-18 receptor complex | A protein complex that binds interleukin-18; comprises an alpha and a beta subunit. |
| interleukin-23 complex | A protein complex that is composed of an interleukin-23 alpha (p19, product of the IL23A gene) and an interleukin-12 beta (p40, product of the IL12B gene) subunit and is secreted into the extracellular space. |
| interleukin-23 receptor complex | A protein complex that binds interleukin-23. The complex comprises two subunits, including the same beta subunit found in the interleukin-12 receptor. |
| interleukin-28 receptor complex | A protein complex that binds interleukin-28 and interleukin-29. Composed of two subunits, IL-28R alpha and IL-10R beta. |
| interleukin-5 receptor complex | A protein complex that binds interleukin-3; comprises an alpha and a beta subunit. The alpha chain is specific to the interleukin-5 receptor, whereas the beta chain is shared with the receptors for granulocyte-macrophage colony-stimulating factor and interleukin-3. |
| interleukin-6 receptor complex | A hexameric protein complex consisting of two molecules each of interleukin-6, interleukin-6 receptor alpha chain, and gp-130. |
| intermediate filament | A cytoskeletal structure that forms a distinct elongated structure, characteristically 10 nm in diameter, that occurs in the cytoplasm of eukaryotic cells. Intermediate filaments form a fibrous system, composed of chemically heterogeneous subunits and involved in mechanically integrating the various components of the cytoplasmic space. Intermediate filaments may be divided into five chemically distinct classes: Type I, acidic keratins; Type II, basic keratins; Type III, including desmin, vimentin and others; Type IV, neurofilaments and related filaments; and Type V, lamins. |
| intermediate filament cytoskeleton | Cytoskeletal structure made from intermediate filaments, typically organized in the cytosol as an extended system that stretches from the nuclear envelope to the plasma membrane. Some intermediate filaments run parallel to the cell surface, while others traverse the cytosol; together they form an internal framework that helps support the shape and resilience of the cell. |
| intermediate-density lipoprotein particle | A triglyceride-rich lipoprotein particle that typically contains APOB100, APOE and APOCs and has a density of 1.006-1.019 g/ml and a diameter of between 25-30 nm. IDL particles are found in blood and are formed by the delipidation of very-low-density lipoprotein particles (VLDL). IDL particles are removed from blood by the liver, following binding to the APOE receptor, or are converted to low-density lipoprotein (LDL). |
| internode region of axon | An axon part that is located between the nodes of Ranvier and surrounded by compact myelin sheath. |
| interphase microtubule organizing center | A microtubule organizing center found in interphase cells, which organize a longitudinal array of three to five MT bundles from the nuclear envelope during interphase. Each MT bundle is composed of two to seven MTs arranged in an antiparallel configuration, with the dynamic MT plus ends extending toward the cell tips and stable minus ends near the nucleus. |
| interphotoreceptor matrix | A specialized extracellularc matrix that surrounds the photoreceptors of the retina and lies between them and the apical surface of the retinal pigment epithelium. The IPM has been implicated in several important activities required for photoreceptor function and maintenance. |
| interstitial matrix | A type of extracellular matrix found in interstitial connective tissue, characterized by the presence of fibronectins, proteoglycans, and types I, III, V, VI, VII and XII collagens. |
| intracellular | The living contents of a cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm. |
| intracellular canaliculus | An apical plasma membrane part that forms a narrow enfolded luminal membrane channel, lined with numerous microvilli, that appears to extend into the cytoplasm of the cell. A specialized network of intracellular canaliculi is a characteristic feature of parietal cells of the gastric mucosa in vertebrates. |
| intracellular cyclic nucleotide activated cation channel complex | A protein complex that forms a transmembrane channel through which cations ions may pass in response to an intracellular cyclic nucleotide binding to the channel complex or one of its constituent parts. |
| intracellular ferritin complex | A ferritin complex located in the cell. Intracellular ferritin complexes contain 24 subunits, in a mixture of L (light) chains and H (heavy) chains. |
| intracellular membrane-bounded organelle | Organized structure of distinctive morphology and function, bounded by a single or double lipid bilayer membrane and occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane. |
| intracellular non-membrane-bounded organelle | Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane and occurring within the cell. Includes ribosomes, the cytoskeleton and chromosomes. |
| intracellular organelle | Organized structure of distinctive morphology and function, occurring within the cell. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton. Excludes the plasma membrane. |
| intracellular organelle lumen | An organelle lumen that is part of an intracellular organelle. |
| intracellular organelle part | A constituent part of an intracellular organelle, an organized structure of distinctive morphology and function, occurring within the cell. Includes constituent parts of the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton but excludes the plasma membrane. |
| intracellular part | Any constituent part of the living contents of a cell; the matter contained within (but not including) the plasma membrane, usually taken to exclude large vacuoles and masses of secretory or ingested material. In eukaryotes it includes the nucleus and cytoplasm. |
| intracellular region of host | That space within the plasma membrane of a host cell. |
| intraciliary transport particle | A nonmembrane-bound oligomeric protein complex that participates in bidirectional transport of molecules (cargo) along axonemal microtubules. |
| intraciliary transport particle a | The smaller subcomplex of the intraciliary transport particle; characterized complexes have molecular weights of 710-760 kDa. |
| intraciliary transport particle b | The larger subcomplex of the intraciliary transport particle; characterized complexes have molecular weights around 550 kDa. |
| intrinsic component of cell outer membrane | The component of the cell outer membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of endoplasmic reticulum membrane | The component of the endoplasmic reticulum membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of endosome membrane | The component of the endosome membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of external side of plasma membrane | The component of a plasma membrane consisting of gene products and protein complexes that penetrate the external side of the plasma membrane only, either directly or via some covalently attached hydrophobic anchor. |
| intrinsic component of golgi membrane | The component of the Golgi membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of membrane | The component of a membrane consisting of the gene products having some covalently attached portion, for example part of a peptide sequence or some other covalently attached group such as a GPI anchor, which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of mitochondrial inner membrane | The component of the mitochondrial inner membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of mitochondrial membrane | The component of the mitochondrial membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of mitochondrial outer membrane | The component of the mitochondrial outer membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of nuclear inner membrane | The component of the nuclear inner membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of nuclear outer membrane | The component of the nuclear outer membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of organelle membrane | The component of the organelle membrane consisting of the gene products that have some covalently attached part (e.g. peptide sequence or GPI anchor) which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of peroxisomal membrane | The component of the peroxisomal membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of plasma membrane | The component of the plasma membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor), which spans or is embedded in one or both leaflets of the membrane. |
| intrinsic component of the cytoplasmic side of the plasma membrane | The component of a plasma membrane consisting of gene products and protein complexes that have some covalently attached part (e.g. peptide sequence or GPI anchor) which is embedded in the cytoplasmic side of the plasma membrane only. |
| invadopodium | A cell projection that emerges from the ECM-facing surface of a cell, is enriched in actin and associated cytoskeletal proteins, and displays localized proteolytic activity toward the substrate. |
| invadopodium membrane | The portion of the plasma membrane surrounding an invadopodium. |
| ion channel complex | A protein complex that spans a membrane and forms a water-filled channel across the phospholipid bilayer allowing selective ion transport down its electrochemical gradient. |
| ionotropic glutamate receptor complex | A multimeric assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand-gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. |
| ipaf inflammasome complex | A protein complex that consists of three components, IPAF, NAIP and caspase-1, and includes among its functions the sensing of flagellin derived from Legionella pneumophila, Salmonella typhimurium, Pseudomonas aeruginosa and Shigella flexneri. |
| isoamylase complex | A protein complex whose composition varies amongst species; in rice it probably exists in a homo-tetramer to homo-hexamer form and in Gram-negative bacteria as a dimer. Functions in the hydrolysis of alpha-(1,6)-D-glucosidic branch linkages. |
| iswi-type complex | Any nuclear protein complex that contains an ATPase subunit of the imitation switch (ISWI) family. ISWI ATPases are involved in assembling chromatin and in sliding and spacing nucleosomes to regulate transcription of nuclear RNA polymerases I, II, and III and also DNA replication, recombination and repair. |
| junctional membrane complex | Complex formed in muscle cells between the membrane of the sarcoplasmic reticulum and invaginations of the plasma membrane (T-tubules). |
| junctional sarcoplasmic reticulum membrane | The part of the sarcoplasmic reticulum membrane that contains calcium release channels, is devoted to calcium release and is juxtaposed to transverse tubule membrane. The junctional sarcoplasmic reticulum membrane consists of the junctional region of the terminal cisterna membrane. |
| juxtaparanode region of axon | A region of an axon near a node of Ranvier that is between the paranode and internode regions. |
| kainate selective glutamate receptor complex | An assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. Kainate receptors are multimeric assemblies of GluR5-7 and KA-1/2 subunits. |
| katanin complex | A complex possessing an activity that couples ATP hydrolysis to the severing of microtubules; usually a heterodimer comprising a catalytic subunit (often 60kDa) and a regulatory subunit (often 80 kDa). |
| keratin filament | A filament composed of acidic and basic keratins (types I and II), typically expressed in epithelial cells. The keratins are the most diverse classes of IF proteins, with a large number of keratin isoforms being expressed. Each type of epithelium always expresses a characteristic combination of type I and type II keratins. |
| kinesin complex | Any complex that includes a dimer of molecules from the kinesin superfamily, a group of related proteins that contain an extended region of predicted alpha-helical coiled coil in the main chain that likely produces dimerization. The native complexes of several kinesin family members have also been shown to contain additional peptides, often designated light chains as all of the noncatalytic subunits that are currently known are smaller than the chain that contains the motor unit. Kinesin complexes generally possess a force-generating enzymatic activity, or motor, which converts the free energy of the gamma phosphate bond of ATP into mechanical work. |
| kinesin i complex | A complex of two kinesin heavy chains and two kinesin light chains. |
| kinesin ii complex | A complex consisting of two distinct motor subunits that form a heterodimer complexed with a third non-motor accessory subunit, the kinesin associated protein or KAP; the KIF3 heterodimer interacts via its C-terminal portion with KAP, which is thought to regulate the binding of the motor to cargo membranes. |
| kinetochore | A multisubunit complex that is located at the centromeric region of DNA and provides an attachment point for the spindle microtubules. |
| kinetochore microtubule | Any of the spindle microtubules that attach to the kinetochores of chromosomes by their plus ends, and maneuver the chromosomes during mitotic or meiotic chromosome segregation. |
| kinocilium | A nonmotile primary cilium that is found at the apical surface of auditory receptor cells. The kinocilium is surrounded by actin-based stereocilia. |
| ku70:ku80 complex | Heterodimeric protein complex composed of a 70 kDa and a 80 kDa subunit, binds DNA through a channel formed by the heterodimer. Functions in DNA double stranded break repair, chromosome maintenance, transcription regulation, V(D)J recombination, and activation of DNA-PK. |
| lamellar body | A membrane-bounded organelle, specialized for the storage and secretion of various substances (surfactant phospholipids, glycoproteins and acid phosphates) which are arranged in the form of tightly packed, concentric, membrane sheets or lamellae. Has some similar properties to, but is distinct from, a lysosome. |
| lamellar body membrane | The lipid bilayer surrounding a lamellar body. A lamellar body is a membrane-bounded organelle, specialized for the storage and secretion of various substances (surfactant phospholipids, glycoproteins and acid phosphates) which are arranged in the form of tightly packed, concentric, membrane sheets or lamellae. Has some similar properties to, but is distinct from, a lysosome. |
| lamellipodium | A thin sheetlike process extended by the leading edge of a crawling fibroblast; contains a dense meshwork of actin filaments. |
| lamellipodium membrane | The portion of the plasma membrane surrounding a lamellipodium. |
| lamin filament | Any of a group of intermediate-filament proteins that form the fibrous matrix on the inner surface of the nuclear envelope. They are classified as lamins A, B and C. |
| laminin complex | A large, extracellular glycoprotein complex composed of three different polypeptide chains, alpha, beta and gamma. Provides an integral part of the structural scaffolding of basement membranes. |
| laminin-1 complex | A laminin complex composed of alpha1, beta1 and gamma1 polypeptide chains. |
| laminin-10 complex | A laminin complex composed of alpha5, beta1 and gamma1 polypeptide chains. |
| laminin-11 complex | A laminin complex composed of alpha5, beta2 and gamma1 polypeptide chains. |
| laminin-2 complex | A laminin complex composed of alpha2, beta1 and gamma1 polypeptide chains. |
| laminin-3 complex | A laminin complex composed of alpha1, beta2 and gamma1 polypeptide chains. |
| laminin-5 complex | A laminin complex composed of alpha3, beta3 and gamma2 polypeptide chains. |
| laminin-8 complex | A laminin complex composed of alpha4, beta1 and gamma1 polypeptide chains. |
| large ribosomal subunit | The larger of the two subunits of a ribosome. Two sites on the ribosomal large subunit are involved in translation, namely the aminoacyl site (A site) and peptidyl site (P site). |
| late endosome | A prelysosomal endocytic organelle differentiated from early endosomes by lower lumenal pH and different protein composition. Late endosomes are more spherical than early endosomes and are mostly juxtanuclear, being concentrated near the microtubule organizing center. |
| late endosome membrane | The lipid bilayer surrounding a late endosome. |
| lateral element | A proteinaceous core found between sister chromatids during meiotic prophase. |
| lateral loop | Non-compact myelin located adjacent to the nodes of Ranvier in a myelin segment. These non-compact regions include cytoplasm from the cell responsible for synthesizing the myelin. Lateral loops are found in the paranodal region adjacent to the nodes of Ranvier, while Schmidt-Lantermann clefts are analogous structures found within the compact myelin internode. |
| lateral plasma membrane | The portion of the plasma membrane at the lateral side of the cell. In epithelial cells, lateral plasma membranes are on the sides of cells which lie at the interface of adjacent cells. |
| leading edge membrane | The portion of the plasma membrane surrounding the leading edge of a motile cell. |
| lewy body | Cytoplasmic, spherical inclusion commonly found in damaged neurons, and composed of abnormally phosphorylated, neurofilament proteins aggregated with ubiquitin and alpha-synuclein. |
| lewy body core | The center portion of a Lewy body. In Parkinson's disease, it contains a matted meshwork of filaments. |
| linc complex | |
| lipid particle | An intracellular non-membrane-bounded organelle comprising a matrix of coalesced lipids surrounded by a phospholipid monolayer. May include associated proteins. |
| lipid tube | A macromolecular complex that contains a tube of lipid surrounded by a protein coat. |
| lipopolysaccharide receptor complex | A multiprotein complex that consists of at least three proteins, CD14, TLR4, and MD-2, each of which is glycosylated and which functions as a lipopolysaccharide (LPS) receptor that primes the innate immune response against bacterial pathogens. |
| longitudinal sarcoplasmic reticulum | The portion of the free sarcoplasmic reticulum consisting of longitudinal tubules that connect terminal cisternae. |
| low-density lipoprotein particle | A lipoprotein particle, rich in cholesterol esters and low in triglycerides that is typically composed of APOB100 and APOE and has a density of 1.02-1.06 g/ml and a diameter of between 20-25 nm. LDL particles are formed from VLDL particles (via IDL) by the loss of triglyceride and gain of cholesterol ester. They transport endogenous cholesterol (and to some extent triglycerides) from peripheral tissues back to the liver. |
| lubac complex | A ubiquitin ligase complex that catalyzes linear head-to-tail polyubiquitin conjugation on its targets. In human the complex consists of RBCK1, RNF31 and SHARPIN, and has an MW of approximately 600 kDa, suggesting a heteromultimeric assembly of its subunits. LUBAC stands for Linear Ubiquitin Chain Assembly Complex. |
| lysosomal lumen | The volume enclosed within the lysosomal membrane. |
| lysosomal membrane | The lipid bilayer surrounding the lysosome and separating its contents from the cell cytoplasm. |
| lysosome | A small lytic vacuole that has cell cycle-independent morphology and is found in most animal cells and that contains a variety of hydrolases, most of which have their maximal activities in the pH range 5-6. The contained enzymes display latency if properly isolated. About 40 different lysosomal hydrolases are known and lysosomes have a great variety of morphologies and functions. |
| lytic vacuole | A vacuole that is maintained at an acidic pH and which contains degradative enzymes, including a wide variety of acid hydrolases. |
| m band | The midline of aligned thick filaments in a sarcomere; location of specific proteins that link thick filaments. Depending on muscle type the M band consists of different numbers of M lines. |
| macromolecular complex | A stable assembly of two or more macromolecules, i.e. proteins, nucleic acids, carbohydrates or lipids, in which the constituent parts function together. |
| macrophage migration inhibitory factor receptor complex | A protein complex that binds macrophage migration inhibitory factor. Comprises CD74 and CD44 cell surface proteins. |
| macropinocytic cup | A cell projection that forms at the site of macropinocytosis, a form of endocytosis that results in the uptake of relatively large amounts of extracellular fluid. The macropinocytic cup membrane selectively excludes certain proteins, such as H36 or PM4C4 in Dictyostelium, and the underlying cytoskeleton is enriched in F-actin and coronin. |
| macropinosome | A membrane-bounded, uncoated intracellular vesicle formed by the process of macropinocytosis. |
| main axon | The main axonal trunk, as opposed to the collaterals. |
| male germ cell nucleus | The nucleus of a male germ cell, a reproductive cell in males. |
| male pronucleus | The pronucleus originating from the spermatozoa that was involved in fertilization. |
| maml1-rbp-jkappa- icn1 complex | A protein complex that consists of the intracellular domain of Notch1 (ICN1), the DNA-binding transcription factor RBP-Jkappa, and the transcriptional coactivator Mastermind-like-1 (MAML1); the complex is involved in transcriptional activation in response to Notch-mediated signaling. |
| manchette | A conical shaped array of microtubules that completely covers the nucleus of a spermatid, thought to be involved in sperm head elongation. |
| mannosyltransferase complex | A complex that posseses mannosyltransferase activity. |
| mast cell granule | Coarse, bluish-black staining cytoplasmic granules, bounded by a plasma membrane and found in mast cells and basophils. Contents include histamine, heparin, chondroitin sulfates, chymase and tryptase. |
| mature chylomicron | A chylomicron that contains apolipoprotein C2 (APOC2), a cofactor for lipoprotein lipase (LPL) activity, and has a mean diameter of 500 nm and density of 0.95g/ml. Mature chylomicron particles transport exogenous (dietary) lipids from the intestines to other body tissues, via the blood and lymph. |
| mcm complex | A hexameric protein complex required for the initiation and regulation of DNA replication. |
| mcm8-mcm9 complex | A hexameric protein complex composed of MCM8 and MCM9 and involved in homologous recombination repair following DNA interstrand cross-links. |
| mediator complex | A protein complex that interacts with the carboxy-terminal domain of the largest subunit of RNA polymerase II and plays an active role in transducing the signal from a transcription factor to the transcriptional machinery. The mediator complex is required for activation of transcription of most protein-coding genes, but can also act as a transcriptional corepressor. The Saccharomyces complex contains several identifiable subcomplexes: a head domain comprising Srb2, -4, and -5, Med6, -8, and -11, and Rox3 proteins; a middle domain comprising Med1, -4, and -7, Nut1 and -2, Cse2, Rgr1, Soh1, and Srb7 proteins; a tail consisting of Gal11p, Med2p, Pgd1p, and Sin4p; and a regulatory subcomplex comprising Ssn2, -3, and -8, and Srb8 proteins. Metazoan mediator complexes have similar modular structures and include homologs of yeast Srb and Med proteins. |
| meiotic cohesin complex | A cohesin complex that mediates sister chromatid cohesion during meiosis; has a subunit composition distinct from that of the mitotic cohesin complex. |
| meiotic spindle | A spindle that forms as part of meiosis. Several proteins, such as budding yeast Spo21p, fission yeast Spo2 and Spo13, and C. elegans mei-1, localize specifically to the meiotic spindle and are absent from the mitotic spindle. |
| melanosome | A tissue-specific, membrane-bounded cytoplasmic organelle within which melanin pigments are synthesized and stored. Melanosomes are synthesized in melanocyte cells. |
| melanosome membrane | The lipid bilayer surrounding a melanosome. |
| membrane | Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. |
| membrane attack complex | A protein complex produced by sequentially activated components of the complement cascade inserted into a target cell membrane and forming a pore leading to cell lysis via ion and water flow. |
| membrane coat | Any of several different proteinaceous coats that can associate with membranes. Membrane coats include those formed by clathrin plus an adaptor complex, the COPI and COPII complexes, and possibly others. They are found associated with membranes on many vesicles as well as other membrane features such as pits and perhaps tubules. |
| membrane part | Any constituent part of a membrane, a double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. |
| membrane raft | Any of the small (10-200 nm), heterogeneous, highly dynamic, sterol- and sphingolipid-enriched membrane domains that compartmentalize cellular processes. Small rafts can sometimes be stabilized to form larger platforms through protein-protein and protein-lipid interactions. |
| membrane region | A membrane that is a part of a larger membrane. Examples include the apical region of the plasma membrane of an epithelial cell and the various regions of the endoplasmic reticulum membrane. |
| membrane-bounded organelle | Organized structure of distinctive morphology and function, bounded by a single or double lipid bilayer membrane. Includes the nucleus, mitochondria, plastids, vacuoles, and vesicles. Excludes the plasma membrane. |
| membrane-bounded vesicle | Any small, fluid-filled, spherical organelle enclosed by a lipid bilayer. |
| membrane-enclosed lumen | The enclosed volume within a sealed membrane or between two sealed membranes. Encompasses the volume enclosed by the membranes of a particular organelle, e.g. endoplasmic reticulum lumen, or the space between the two lipid bilayers of a double membrane surrounding an organelle, e.g. nuclear envelope lumen. |
| meprin a complex | A protein complex that is located in the cell membrane, and is involved in the metabolism of peptides, including neuropeptides. The complex has metalloendopeptidase activity that catalyzes the hydrolysis of protein and peptide substrates, preferentially on carboxyl side of hydrophobic residues. |
| methionine adenosyltransferase complex | A multimeric enzyme complex composed of variable numbers of catalytic alpha subunits, and noncatalytic beta subunits. The beta subunits are believed to have a regulatory function. The enzyme complex catalyzes the synthesis of S-adenosylmethionine (AdoMet), which is the major methyl group donor, participating in the methylation of proteins, DNA, RNA, phospholipids, and other small molecules. |
| methylosome | A large (20 S) protein complex that possesses protein arginine methyltransferase activity and modifies specific arginines to dimethylarginines in the arginine- and glycine-rich domains of several spliceosomal Sm proteins, thereby targeting these proteins to the survival of motor neurons (SMN) complex for assembly into small nuclear ribonucleoprotein (snRNP) core particles. Proteins found in the methylosome include the methyltransferase JBP1 (PRMT5), pICln (CLNS1A), MEP50 (WDR77), and unmethylated forms of SM proteins that have RG domains. |
| methyltransferase complex | A protein complex that possesses methyltransferase activity. |
| mhc class i peptide loading complex | A large, multisubunit complex which consists of the MHC class I-beta 2 microglobulin dimer, the transporter associated with antigen presentation (TAP), tapasin (an MHC-encoded membrane protein), the chaperone calreticulin and the thiol oxidoreductase ERp57. Functions in the assembly of peptides with newly synthesized MHC class I molecules. |
| mhc class i protein complex | A transmembrane protein complex composed of a MHC class I alpha chain and an invariant beta2-microglobin chain, and with or without a bound peptide antigen. Class I here refers to classical class I molecules. |
| mhc class ii protein complex | A transmembrane protein complex composed of an MHC class II alpha and MHC class II beta chain, and with or without a bound peptide or polysaccharide antigen. |
| mhc protein complex | A transmembrane protein complex composed of an MHC alpha chain and, in most cases, either an MHC class II beta chain or an invariant beta2-microglobin chain, and with or without a bound peptide, lipid, or polysaccharide antigen. |
| micro-ribonucleoprotein complex | A complex containing both protein and micro-RNA (miRNA) molecules. miRNAs are approximately 22 nucleotide noncoding RNAs derived from endogenous genes; they are processed from the stem of a longer hairpin like structure termed a pre-miRNA. |
| microbody | Cytoplasmic organelles, spherical or oval in shape, that are bounded by a single membrane and contain oxidative enzymes, especially those utilizing hydrogen peroxide (H2O2). |
| microbody lumen | The volume enclosed by the membranes of a microbody. |
| microbody membrane | The lipid bilayer surrounding a microbody. |
| microbody part | Any constituent part of a microbody, a cytoplasmic organelle, spherical or oval in shape, that is bounded by a single membrane and contains oxidative enzymes, especially those utilizing hydrogen peroxide (H2O2). |
| microfibril | Extracellular matrix components occurring independently or along with elastin. Thought to have force-bearing functions in tendon. In addition to fibrillins, microfibrils may contain other associated proteins. |
| microspike | A dynamic, actin-rich projection extending from the surface of a migrating animal cell. |
| microtubule | Any of the long, generally straight, hollow tubes of internal diameter 12-15 nm and external diameter 24 nm found in a wide variety of eukaryotic cells; each consists (usually) of 13 protofilaments of polymeric tubulin, staggered in such a manner that the tubulin monomers are arranged in a helical pattern on the microtubular surface, and with the alpha/beta axes of the tubulin subunits parallel to the long axis of the tubule; exist in equilibrium with pool of tubulin monomers and can be rapidly assembled or disassembled in response to physiological stimuli; concerned with force generation, e.g. in the spindle. |
| microtubule associated complex | Any multimeric complex connected to a microtubule. |
| microtubule bundle | An arrangement of closely apposed microtubules running parallel to each other. |
| microtubule cytoskeleton | The part of the cytoskeleton (the internal framework of a cell) composed of microtubules and associated proteins. |
| microtubule organizing center | An intracellular structure that can catalyze gamma-tubulin-dependent microtubule nucleation and that can anchor microtubules by interacting with their minus ends, plus ends or sides. |
| microtubule organizing center attachment site | A region of the nuclear envelope to which a microtubule organizing center (MTOC) attaches; protein complexes embedded in the nuclear envelope mediate direct or indirect linkages between the microtubule cytoskeleton and the nuclear envelope. |
| microtubule organizing center part | Any constituent part of a microtubule organizing center, a region in a eukaryotic cell, such as a centrosome or basal body, from which microtubules grow. |
| microtubule plus-end | The growing (plus) end of a microtubule. In vitro, microtubules polymerize more quickly at the plus end than at the minus end. In vivo, microtubule growth occurs only at the plus end, and the plus end switches between periods of growth and shortening, a behavior known as dynamic instability. |
| microvillus | Thin cylindrical membrane-covered projections on the surface of an animal cell containing a core bundle of actin filaments. Present in especially large numbers on the absorptive surface of intestinal cells. |
| microvillus membrane | The portion of the plasma membrane surrounding a microvillus. |
| midbody | A thin cytoplasmic bridge formed between daughter cells at the end of cytokinesis. The midbody forms where the contractile ring constricts, and may persist for some time before finally breaking to complete cytokinesis. |
| mis12/mind type complex | A multiprotein kinetochore subcomplex that binds to centromeric chromatin and forms part of the inner kinetochore. It helps to recruit outer kinetochore subunits that will bind to microtubules. In humans, it consists of MIS12, DSN1, NSL1 and PMF1. |
| mismatch repair complex | Any complex formed of proteins that act in mismatch repair. |
| mitochondrial alpha-ketoglutarate dehydrogenase complex | Mitochondrial complex that possesses alpha-ketoglutarate dehydrogenase activity. |
| mitochondrial chromosome | A chromosome found in the mitochondrion of a eukaryotic cell. |
| mitochondrial crista | Any of the inward folds of the mitochondrial inner membrane. Their number, extent, and shape differ in mitochondria from different tissues and organisms. They appear to be devices for increasing the surface area of the mitochondrial inner membrane, where the enzymes of electron transport and oxidative phosphorylation are found. Their shape can vary with the respiratory state of the mitochondria. |
| mitochondrial degradosome | A mitochondrial protein complex with 3' to 5' exoribonuclease activity that participates in intron-independent turnover and processing of mitochondrial transcripts. In humans, the mitochondrial degradosome is a pentameric complex, and in yeast it exists as a heterodimer. |
| mitochondrial endopeptidase clp complex | A Clp endopeptidase complex located in the mitochondrion. |
| mitochondrial envelope | The double lipid bilayer enclosing the mitochondrion and separating its contents from the cell cytoplasm; includes the intermembrane space. |
| mitochondrial fatty acid beta-oxidation multienzyme complex | A complex that includes the long-chain 3-hydroxyacyl-CoA dehydrogenase and long-chain enoyl-CoA hydratase activities in two subunits (alpha and beta), catalyzing two steps of the fatty acid beta-oxidation cycle within the mitochondrial matrix. |
| mitochondrial inner membrane | The inner, i.e. lumen-facing, lipid bilayer of the mitochondrial envelope. It is highly folded to form cristae. |
| mitochondrial inner membrane peptidase complex | Protease complex of the mitochondrial inner membrane, consisting of at least two subunits, involved in processing of both nuclear- and mitochondrially-encoded proteins targeted to the intermembrane space. |
| mitochondrial inner membrane presequence translocase complex | The protein transport machinery of the mitochondrial inner membrane that contains three essential Tim proteins: Tim17 and Tim23 are thought to build a preprotein translocation channel while Tim44 interacts transiently with the matrix heat-shock protein Hsp70 to form an ATP-driven import motor. |
| mitochondrial intermembrane space | The region between the inner and outer lipid bilayers of the mitochondrial envelope. |
| mitochondrial intermembrane space protein transporter complex | Soluble complex of the mitochondrial intermembrane space composed of various combinations of small Tim proteins; acts as a protein transporter to guide proteins to the Tim22 complex for insertion into the mitochondrial inner membrane. |
| mitochondrial large ribosomal subunit | The larger of the two subunits of a mitochondrial ribosome. Two sites on the ribosomal large subunit are involved in translation: the aminoacyl site (A site) and peptidyl site (P site). |
| mitochondrial matrix | The gel-like material, with considerable fine structure, that lies in the matrix space, or lumen, of a mitochondrion. It contains the enzymes of the tricarboxylic acid cycle and, in some organisms, the enzymes concerned with fatty acid oxidation. |
| mitochondrial membrane | Either of the lipid bilayers that surround the mitochondrion and form the mitochondrial envelope. |
| mitochondrial membrane part | Any constituent part of a mitochondrial membrane, either of the lipid bilayers that surround the mitochondrion and form the mitochondrial envelope. |
| mitochondrial nucleoid | The region of a mitochondrion to which the DNA is confined. |
| mitochondrial outer membrane | The outer, i.e. cytoplasm-facing, lipid bilayer of the mitochondrial envelope. |
| mitochondrial outer membrane translocase complex | A large complex of the mitochondrial outer membrane that mediates transport of proteins into all mitochondrial compartments. |
| mitochondrial part | Any constituent part of a mitochondrion, a semiautonomous, self replicating organelle that occurs in varying numbers, shapes, and sizes in the cytoplasm of virtually all eukaryotic cells. It is notably the site of tissue respiration. |
| mitochondrial permeability transition pore complex | A protein complex that connects the inner and outer membranes of animal mitochondria and acts as a pore that can open transiently to allow free diffusion of solutes between the mitochondrial matrix and the cytosol. The pore complex is formed of the voltage-dependent anion channel (VDAC), the adenine nucleotide translocase (ANT) and cyclophilin-D (CyP-D). |
| mitochondrial proton-transporting atp synthase complex | A proton-transporting ATP synthase complex found in the mitochondrial membrane. |
| mitochondrial proton-transporting atp synthase complex, catalytic core f(1) | The catalytic sector of the mitochondrial hydrogen-transporting ATP synthase; it comprises the catalytic core and central stalk, and is peripherally associated with the mitochondrial inner membrane when the entire ATP synthase is assembled. |
| mitochondrial proton-transporting atp synthase complex, coupling factor f(o) | All non-F1 subunits of the mitochondrial hydrogen-transporting ATP synthase, including integral and peripheral mitochondrial inner membrane proteins. |
| mitochondrial proton-transporting atp synthase, catalytic core | The hexamer, comprising three alpha and three beta subunits, that possesses the catalytic activity of the mitochondrial hydrogen-transporting ATP synthase. |
| mitochondrial pyruvate dehydrogenase complex | Complex that carries out the oxidative decarboxylation of pyruvate to form acetyl-CoA in eukaryotes; includes subunits possessing three catalytic activities: pyruvate dehydrogenase (E1), dihydrolipoamide S-acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). The This Eukaryotic form usually contains more subunits than its bacterial counterpart; for example, one known complex contains 30 E1 dimers, 60 E2 monomers, and 6 E3 dimers as well as a few copies of pyruvate dehydrogenase kinase and pyruvate dehydrogenase phosphatase. |
| mitochondrial respiratory chain | The protein complexes that form the mitochondrial electron transport system (the respiratory chain), associated with the inner mitochondrial membrane. The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient. |
| mitochondrial respiratory chain complex i | A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. It contains about 25 different polypeptide subunits, including NADH dehydrogenase (ubiquinone), flavin mononucleotide and several different iron-sulfur clusters containing non-heme iron. The iron undergoes oxidation-reduction between Fe(II) and Fe(III), and catalyzes proton translocation linked to the oxidation of NADH by ubiquinone. |
| mitochondrial respiratory chain complex ii | A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains the four polypeptide subunits of succinate dehydrogenase, flavin-adenine dinucleotide and iron-sulfur. Catalyzes the oxidation of succinate by ubiquinone. Connects the TCA cycle with the respiratory chain. |
| mitochondrial respiratory chain complex iii | A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains about 10 polypeptide subunits including four redox centers: cytochrome b/b6, cytochrome c1 and an 2Fe-2S cluster. Catalyzes the oxidation of ubiquinol by oxidized cytochrome c1. |
| mitochondrial respiratory chain complex iv | A protein complex located in the mitochondrial inner membrane that forms part of the mitochondrial respiratory chain. Contains the 13 polypeptide subunits of cytochrome c oxidase, including cytochrome a and cytochrome a3. Catalyzes the oxidation of reduced cytochrome c by dioxygen (O2). |
| mitochondrial ribosome | A ribosome found in the mitochondrion of a eukaryotic cell; contains a characteristic set of proteins distinct from those of cytosolic ribosomes. |
| mitochondrial small ribosomal subunit | The smaller of the two subunits of a mitochondrial ribosome. |
| mitochondrial sorting and assembly machinery complex | A large complex of the mitochondrial outer membrane that mediates sorting of some imported proteins to the outer membrane and their assembly in the membrane; functions after import of incoming proteins by the mitochondrial outer membrane translocase complex. |
| mitochondrial tricarboxylic acid cycle enzyme complex | Any of the heteromeric enzymes, located in the mitochondrion, that act in the tricarboxylic acid (TCA) cycle. |
| mitochondrion | A semiautonomous, self replicating organelle that occurs in varying numbers, shapes, and sizes in the cytoplasm of virtually all eukaryotic cells. It is notably the site of tissue respiration. |
| mitotic cohesin complex | A cohesin complex that mediates sister chromatid cohesion during mitosis; has a subunit composition distinct from that of the meiotic cohesin complex. |
| mitotic spindle | A spindle that forms as part of mitosis. Mitotic and meiotic spindles contain distinctive complements of proteins associated with microtubules. |
| mitotic spindle midzone | The area in the center of the anaphase spindle consisting of microtubules, microtubule bundling factors and kinesin motors where the spindle microtubules from opposite poles overlap in an antiparallel manner. |
| mitotic spindle pole | Either of the ends of a mitotic spindle, a spindle that forms as part of mitosis, where spindle microtubules are organized; usually contains a microtubule organizing center and accessory molecules, spindle microtubules and astral microtubules. |
| mll1 complex | A protein complex that can methylate lysine-4 of histone H3. MLL1/MLL is the catalytic methyltransferase subunit, and the complex also contains the core components ASH2L, HCFC1/HCF1 WDR5 and RBBP5. |
| mll1/2 complex | A protein complex that can methylate lysine-4 of histone H3, and which contains either of the protein subunits MLL1 or MLL2 in human, or equivalent in other species. |
| mll5-l complex | A protein complex that can methylate lysine-4 of histone H3 and plays an essential role in retinoic-acid-induced granulopoiesis. MLL5 is the catalytic methyltransferase subunit, and the complex also contains serine/threonine kinase 38 (STK38), protein phosphatase 1 catalytic subunits, the host cell factor-1 N-terminal subunit, beta-actin, and O-GlcNAc transferase; the human genes encoding the subunits are MLL5, STK38, PPP1CA, PPP1CB, PPP1CC, HCFC1, ACTB and OGT, respectively. |
| mmxd complex | A protein complex that contains the proteins MMS19, MIP18 and XPD, localizes to mitotic spindle during mitosis, and is required for proper chromosome segregation. |
| molybdopterin synthase complex | A protein complex that possesses molybdopterin synthase activity. In E. coli, the complex is a heterotetramer consisting of two MoaD and two MoaE subunits. |
| monomeric iga immunoglobulin complex | A protein complex composed of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| motile cilium | A cilium which has a variable arrangement of axonemal microtubules, contains molecular motors, and beats with a characteristic whip-like pattern that promotes cell motility or transport of fluids and other cells across a cell surface. Motile cilia are typically found in multiple copies on epithelial cells that line the lumenal ducts of various tissues. Motile cilia may also function as sensory organelles. |
| motile primary cilium | A primary cilium which may contain a variable array of axonemal microtubules and also contains molecular motors. Motile primary cilia display a distinct twirling motion that directs fluid flow asymmetrically across the cellular surface to affect asymmetric body plan organization. |
| moz/morf histone acetyltransferase complex | A histone acetyltransferase complex that has histone H3 acetyltransferase and coactivator activities. Subunits of the human complex include MYST3/MOZ, MYST4/MORF, ING5, EAF6 and one of BRPF1, BRD1/BRPF2 and BRPF3. |
| mpp7-dlg1-lin7 complex | A heterotrimeric protein complex formed by the association of MMP7, DLG1 and either LIN7A or LIN7C; regulates the stability and localization of DLG1 to cell junctions. |
| mre11 complex | Trimeric protein complex that possesses endonuclease activity; involved in meiotic recombination, DNA repair and checkpoint signaling. In Saccharomyces cerevisiae, the complex comprises Mre11p, Rad50p, and Xrs2p; complexes identified in other species generally contain proteins orthologous to the Saccharomyces cerevisiae proteins. |
| mrna cap binding complex | Any protein complex that binds to an mRNA cap at any time in the lifetime of the mRNA. |
| mrna cleavage and polyadenylation specificity factor complex | A multisubunit complex that binds to the canonical AAUAAA hexamer and to U-rich upstream sequence elements on the pre-mRNA, thereby stimulating the otherwise weakly active and nonspecific polymerase to elongate efficiently RNAs containing a poly(A) signal. |
| mrna cleavage factor complex | Any macromolecular complex involved in cleavage or polyadenylation of mRNA molecules. |
| msl complex | A histone acetyltransferase complex that catalyzes the acetylation of a histone H4 lysine residue at position 16. In human, it contains the catalytic subunit MOF, and MSL1, MSL2 and MSL3. |
| mucus layer | An extracellular region part that consists of a protective layer of mucus secreted by epithelial cells lining tubular organs of the body such as the colon or secreted into fluids such as saliva. Mucus is a viscous slimy secretion consisting of mucins (i.e. highly glycosylated mucin proteins) and various inorganic salts dissolved in water, with suspended epithelial cells and leukocytes. |
| multimeric ribonuclease p complex | A ribonuclease P complex that generally contains a single RNA molecule and several protein molecules. Examples of this complex are found in Archaeal species. |
| multivesicular body | A type of late endosome in which regions of the limiting endosomal membrane invaginate to form internal vesicles; membrane proteins that enter the internal vesicles are sequestered from the cytoplasm. |
| multivesicular body membrane | The lipid bilayer surrounding a multivesicular body. |
| muscle myosin complex | A filament of myosin found in a muscle cell of any type. |
| muscle tendon junction | A cell-substrate junction found at the terminal anchorage site of skeletal muscle cells to tendons. |
| muscle thin filament tropomyosin | A form of the tropomyosin dimer found associated with actin and the troponin complex in muscle thin filaments. |
| mutlalpha complex | A heterodimer involved in the recognition of base-base and small insertion/deletion mismatches. In human the complex consists of two subunits, MLH1 and PMS2. |
| mutsalpha complex | A heterodimer involved in the recognition and repair of base-base and small insertion/deletion mismatches. In human the complex consists of two subunits, MSH2 and MSH6. |
| mutsbeta complex | A heterodimer involved in binding to and correcting insertion/deletion mutations. In human the complex consists of two subunits, MSH2 and MSH3. |
| myb complex | A multisubunit complex consisting of Myb and other proteins that regulates site specific DNA replication, gene amplification and transcriptional repression. |
| myelin sheath | The cylindrical covering on the axons of some neurons; it consists of concentric layers of myelin, formed in the peripheral nervous system by the plasma membrane of Schwann cells, and in the central nervous system by oligodendrocytes. It is interrupted at intervals along its length by gaps known as nodes of Ranvier. Myelin is an electrical insulator that serves to speed the conduction of nerve impulses. |
| myelin sheath abaxonal region | The region of the myelin sheath furthest from the axon. |
| myelin sheath adaxonal region | The region of the myelin sheath nearest to the axon. |
| myofibril | The contractile element of skeletal and cardiac muscle; a long, highly organized bundle of actin, myosin, and other proteins that contracts by a sliding filament mechanism. |
| myofilament | Any of the smallest contractile units of a myofibril (striated muscle fiber). |
| myosin complex | A protein complex, formed of one or more myosin heavy chains plus associated light chains and other proteins, that functions as a molecular motor; uses the energy of ATP hydrolysis to move actin filaments or to move vesicles or other cargo on fixed actin filaments; has magnesium-ATPase activity and binds actin. Myosin classes are distinguished based on sequence features of the motor, or head, domain, but also have distinct tail regions that are believed to bind specific cargoes. |
| myosin filament | A protein complex containing myosin heavy chains, plus associated light chains and other proteins, in which the myosin heavy chains are arranged into a filament. |
| myosin i complex | A myosin complex containing a class I myosin heavy chain and associated light chains; myosin I heavy chains are single-headed, possess tails of various lengths, and do not self-associate into bipolar filaments; myosin I complexes are involved in diverse processes related to membrane traffic and cell movement. |
| myosin ii complex | A myosin complex containing two class II myosin heavy chains, two myosin essential light chains and two myosin regulatory light chains. Also known as classical myosin or conventional myosin, the myosin II class includes the major muscle myosin of vertebrate and invertebrate muscle, and is characterized by alpha-helical coiled coil tails that self assemble to form a variety of filament structures. |
| myosin vii complex | A myosin complex containing a dimer of class VII myosin heavy chains and associated light chains. Myosin VII (240 kDa) is predicted to be a dimeric molecule with 5 IQ motifs and a tail region with a short stretch of coiled coil followed by two myosin-tail homology (MyTH4) domains, two talin-binding (FERM) domains and an SH3-domain. |
| n-methyl-d-aspartate selective glutamate receptor complex | An assembly of four or five subunits which form a structure with an extracellular N-terminus and a large loop that together form the ligand binding domain. The C-terminus is intracellular. The ionotropic glutamate receptor complex itself acts as a ligand gated ion channel; on binding glutamate, charged ions pass through a channel in the center of the receptor complex. NMDA receptors are composed of assemblies of NR1 subunits (Figure 3) and NR2 subunits, which can be one of four separate gene products (NR2A-D). Expression of both subunits are required to form functional channels. The glutamate binding domain is formed at the junction of NR1 and NR2 subunits. NMDA receptors are permeable to calcium ions as well as being permeable to other ions. Thus NMDA receptor activation leads to a calcium influx into the post-synaptic cells, a signal thought to be crucial for the induction of NMDA-receptor dependent LTP and LTD. |
| n-terminal protein acetyltransferase complex | A complex that catalyzes the transfer of an acetyl group to the N-terminal residue of a protein acceptor molecule. |
| nadh dehydrogenase complex | An integral membrane complex that possesses NADH oxidoreductase activity. The complex is one of the components of the electron transport chain. It catalyzes the transfer of a pair of electrons from NADH to a quinone. |
| nadph oxidase complex | A enzyme complex of which the core is a heterodimer composed of a light (alpha) and heavy (beta) chain, and requires several other water-soluble proteins of cytosolic origin for activity. Functions in superoxide generation by the NADPH-dependent reduction of O2. |
| nascent polypeptide-associated complex | A heterodimeric protein complex that can reversibly bind to ribosomes, and is located in direct proximity to newly synthesized polypeptide chains as they emerge from the ribosome. |
| nata complex | A conserved complex that catalyzes the transfer of an acetyl group to an N-terminal Ser, Ala, Gly, or Thr residue of a protein acceptor molecule. In Saccharomyces the complex includes Nat1p and Ard1p, and may contain additional proteins. |
| natc complex | A conserved complex that catalyzes the transfer of an acetyl group to the N-terminal residue of a protein acceptor molecule that has a Met-Ile, Met-Leu, Met-Trp, or Met-Phe N-terminus. In Saccharomyces the complex includes Mak3p, Mak10p, and Mak31p. |
| nbaf complex | A SWI/SNF-type complex that is found in post-mitotic neurons, and in human contains actin and proteins encoded by the ARID1A/BAF250A or ARID1B/BAF250B, SMARCD1/BAF60A, SMARCD3/BAF60C, SMARCA2/BRM/BAF190B, SMARCA4/BRG1/BAF190A, SMARCB1/BAF47, SMARCC1/BAF155, SMARCE1/BAF57, SMARCC2/BAF170, DPF1/BAF45B, DPF3/BAF45C, ACTL6B/BAF53B genes. The nBAF complex along with CREST plays a role regulating the activity of genes essential for dendrite growth. |
| ndc80 complex | A protein complex conserved among eukaryotes that forms part of the kinetochore and plays an essential role in forming stable kinetochore-microtubule attachments. The complex contains proteins known in several species, including budding and fission yeasts, as Ndc80p, Nuf2p, Spc24p, and Spc25p. In vertebrates it is part of the outer plate of the kinetochore. |
| nelf complex | A complex of five proteins, designated NELF-A, -B, -C, -D, and -E in human, that can physically associate with RNP polymerase II to induce transcriptional pausing. |
| nem1-spo7 phosphatase complex | A protein serine/threonine phosphatase complex that is involved in nuclear envelope organization, and contains proteins known in budding yeast as Nem1p and Spo7p. |
| network-forming collagen trimer | A collagen trimer that forms networks. |
| neurofibrillary tangle | Intracellular knot or clump of neurofibrils seen in the cerebral cortex in Alzheimer's disease. |
| neurofilament | A type of intermediate filament found in the core of neuronal axons. Neurofilaments are heteropolymers composed of three type IV polypeptides: NF-L, NF-M, and NF-H (for low, middle, and high molecular weight). Neurofilaments are responsible for the radial growth of an axon and determine axonal diameter. |
| neurofilament cytoskeleton | Intermediate filament cytoskeletal structure that is made up of neurofilaments. Neurofilaments are specialized intermediate filaments found in neurons. |
| neuromuscular junction | The junction between the axon of a motor neuron and a muscle fiber. In response to the arrival of action potentials, the presynaptic button releases molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane of the muscle fiber, leading to a change in post-synaptic potential. |
| neuron part | Any constituent part of a neuron, the basic cellular unit of nervous tissue. A typical neuron consists of a cell body (often called the soma), an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. |
| neuron projection | A prolongation or process extending from a nerve cell, e.g. an axon or dendrite. |
| neuron projection membrane | The portion of the plasma membrane surrounding a neuron projection. |
| neuron projection terminus | The specialized, terminal region of a neuron projection such as an axon or a dendrite. |
| neuron spine | A small membranous protrusion, often ending in a bulbous head and attached to the neuron by a narrow stalk or neck. |
| neuronal cell body | The portion of a neuron that includes the nucleus, but excludes cell projections such as axons and dendrites. |
| neuronal cell body membrane | The plasma membrane of a neuron cell body - excludes the plasma membrane of cell projections such as axons and dendrites. |
| neuronal ribonucleoprotein granule | A ribonucleoprotein complex that is found in the cytoplasm of axons and dendrites, and transports translationally silenced mRNAs to dendritic synapses, where they are released and translated in response to specific exogenous stimuli. |
| new growing cell tip | A cell tip that was newly formed at the last cell division, and that has started to grow after the cell has activated bipolar cell growth (i.e. in which new end take-off, NETO, has taken place). New end take-off is when monopolar cells initiate bipolar growth. |
| nlrp1 inflammasome complex | A protein complex that consists of two components, NLRP1 (NALP1) and caspase-1 or caspase-5. The exact mechanisms of NLRP1 activation remain obscure, but potassium ion efflux appears to be essential. |
| nlrp3 inflammasome complex | A protein complex that consists of three components, NLRP3 (NALP3), PYCARD and caspase-1. It is activated upon exposure to whole pathogens, as well as a number of structurally diverse pathogen- and danger-associated molecular patterns (PAMPs and DAMPs) and environmental irritants. Whole pathogens demonstrated to activate the NLRP3 inflammasome complex include the fungi Candida albicans and Saccharomyces cerevisiae, bacteria that produce pore-forming toxins, including Listeria monocytogenes and Staphylococcus aureus, and viruses such as Sendai virus, adenovirus, and influenza virus. |
| nls-dependent protein nuclear import complex | A protein complex which usually consists of three components, e.g. in Xenopus, the importin alpha and beta-subunits and any protein which has a nuclear localization sequence (NLS). The complex acts to import proteins with an NLS into the nucleus through a nuclear pore. |
| noc complex | Any of several heterodimers containing one or two Noc proteins, associated with preribosomal complexes; involved in ribosome biogenesis. |
| noc1p-noc2p complex | A heterodimer associated with 90S and 66S preribosomes. Predominantly, but not exclusively, nucleolar; involved in ribosomal large subunit biogenesis. |
| noc4p-nop14p complex | A heterodimer associated with precursors of the eukaryotic small ribosomal subunit, including the 90S preribosome; involved in small subunit biogenesis. |
| node of ranvier | An axon part that is a gap in the myelin where voltage-gated sodium channels cluster and saltatory conduction is executed. |
| non-membrane-bounded organelle | Organized structure of distinctive morphology and function, not bounded by a lipid bilayer membrane. Includes ribosomes, the cytoskeleton and chromosomes. |
| nonhomologous end joining complex | A protein complex that plays a role in DNA double-strand break repair via nonhomologous end joining. Such complexes typically contain a specialized DNA ligase (e.g. Lig4 in eukaryotes) and one or more proteins that bind to DNA ends. |
| nonmotile primary cilium | A primary cilium which contains a variable array of axonemal microtubules but does not contain molecular motors. Nonmotile primary cilia are found on many different cell types and function as sensory organelles that concentrate and organize sensory signaling molecules. |
| nos2-cd74 complex | A protein complex comprising nitric oxide synthase 2 and CD74. This stable complex formation is thought to prevent CD74 degradation by caspases. |
| npbaf complex | A SWI/SNF-type complex that is found in neural stem or progenitor cells, and in human contains actin and proteins encoded by the ARID1A/BAF250A or ARID1B/BAF250B, SMARCD1/BAF60A, SMARCD3/BAF60C, SMARCA2/BRM/BAF190B, SMARCA4/BRG1/BAF190A, SMARCB1/BAF47, SMARCC1/BAF155, SMARCE1/BAF57, SMARCC2/BAF170, PHF10/BAF45A, ACTL6A/BAF53A genes. The npBAF complex is essential for the self-renewal/proliferative capacity of the multipotent neural stem cells. |
| nua4 histone acetyltransferase complex | A complex having histone acetylase activity on chromatin, as well as ATPase, DNA helicase and structural DNA binding activities. The complex is thought to be involved in double-strand DNA break repair. Subunits of the human complex include HTATIP/TIP60, TRRAP, RUVBL1, BUVBL2, beta-actin and BAF53/ACTL6A. In yeast, the complex has 13 subunits, including the catalytic subunit Esa1 (homologous to human Tip60). |
| nuclear body | Extra-nucleolar nuclear domains usually visualized by confocal microscopy and fluorescent antibodies to specific proteins. |
| nuclear cap binding complex | A conserved heterodimeric protein complex that binds to the 5' terminal cap structure m7G(5')ppp(5')N of nascent eukaryotic RNA polymerase II transcripts such as pre-mRNA and U snRNA. The consists of proteins known as CBP20 and CBP80, binds to cap structures in the nucleus, and is involved in pre-mRNA splicing, 3'-end formation, and RNA nuclear export. |
| nuclear chromatin | The ordered and organized complex of DNA, protein, and sometimes RNA, that forms the chromosome in the nucleus. |
| nuclear chromosome | A chromosome found in the nucleus of a eukaryotic cell. |
| nuclear chromosome part | Any constituent part of a nuclear chromosome, a chromosome found in the nucleus of a eukaryotic cell. |
| nuclear chromosome, telomeric region | The terminal region of a linear chromosome in the nucleus that includes the telomeric DNA repeats and associated proteins. |
| nuclear cohesin complex | A cohesin complex required for cohesion between sister chromatids that remain in the nucleus. |
| nuclear condensin complex | A multisubunit protein complex that plays a central role in the condensation of chromosomes that remain in the nucleus. |
| nuclear cyclin-dependent protein kinase holoenzyme complex | Cyclin-dependent protein kinase (CDK) complex found in the nucleus. |
| nuclear dna-directed rna polymerase complex | A protein complex, located in the nucleus, that possesses DNA-directed RNA polymerase activity. |
| nuclear envelope | The double lipid bilayer enclosing the nucleus and separating its contents from the rest of the cytoplasm; includes the intermembrane space, a gap of width 20-40 nm (also called the perinuclear space). |
| nuclear envelope lumen | The region between the two lipid bilayers of the nuclear envelope; 20-40 nm wide. |
| nuclear euchromatin | The dispersed less dense form of chromatin in the interphase nucleus. It exists in at least two forms, a some being in the form of transcriptionally active chromatin which is the least condensed, while the rest is inactive euchromatin which is more condensed than active chromatin but less condensed than heterochromatin. |
| nuclear exosome (rnase complex) | Complex of 3'-5' exoribonucleases found in the nucleus. |
| nuclear heterochromatin | A condensed form of chromatin, occurring in the nucleus during interphase, that stains strongly with basophilic dyes. The DNA of heterochromatin is typically replicated at a later stage in the cell-division cycle than euchromatin. |
| nuclear inclusion body | An intranuclear focus at which aggregated proteins have been sequestered. |
| nuclear inner membrane | The inner, i.e. lumen-facing, lipid bilayer of the nuclear envelope. |
| nuclear lamina | The fibrous, electron-dense layer lying on the nucleoplasmic side of the inner membrane of a cell nucleus, composed of lamin filaments. The polypeptides of the lamina are thought to be concerned in the dissolution of the nuclear envelope and its re-formation during mitosis. The lamina is composed of lamin A and lamin C filaments cross-linked into an orthogonal lattice, which is attached via lamin B to the inner nuclear membrane through interactions with a lamin B receptor, an IFAP, in the membrane. |
| nuclear lumen | The volume enclosed by the nuclear inner membrane. |
| nuclear matrix | The dense fibrillar network lying on the inner side of the nuclear membrane. |
| nuclear meiotic cohesin complex | A cohesin complex that mediates sister chromatid cohesion in the nucleus during meiosis; has a subunit composition distinct from that of the meiotic cohesin complex. |
| nuclear membrane | Either of the lipid bilayers that surround the nucleus and form the nuclear envelope; excludes the intermembrane space. |
| nuclear membrane part | Any constituent part of the nuclear membrane, the envelope that surrounds the nucleus of eukaryotic cells. |
| nuclear nucleosome | A complex comprised of DNA wound around a multisubunit core and associated proteins, which forms the primary packing unit of DNA in the nucleus into higher order structures. |
| nuclear origin of replication recognition complex | A multisubunit complex that is located at the replication origins of a chromosome in the nucleus. |
| nuclear outer membrane | The outer, i.e. cytoplasm-facing, lipid bilayer of the nuclear envelope; continuous with the endoplasmic reticulum of the cell and sometimes studded with ribosomes. |
| nuclear outer membrane-endoplasmic reticulum membrane network | The continuous network of membranes encompassing the nuclear outer membrane and the endoplasmic reticulum membrane. |
| nuclear part | Any constituent part of the nucleus, a membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. |
| nuclear pericentric heterochromatin | Nuclear heterochromatin that is located adjacent to the CENP-A rich centromere 'central core' and characterized by the modified histone H3K9me3. |
| nuclear periphery | The portion of the nuclear lumen proximal to the inner nuclear membrane. |
| nuclear pore | Any of the numerous similar discrete openings in the nuclear envelope of a eukaryotic cell, where the inner and outer nuclear membranes are joined. |
| nuclear pore nuclear basket | A filamentous, cage-like assembly on the nuclear face of the nuclear pore complex (NPC). In S. cerevisiae, Mlp1p and Mlp2p are two major components of the NPC nuclear basket. In vertebrates, Tpr is a major component. |
| nuclear pore outer ring | A subcomplex of the nuclear pore complex (NPC) that forms the outer rings of the core scaffold, a lattice-like structure that gives the NPC its shape and strength. In S. cerevisiae, the two outer rings each contain multiple copies of the following proteins: Nup133p, Nup120p, Nup145Cp, Nup85p, Nup84p, Seh1p, and Sec13p. In vertebrates, the two outer rings each contain multiple copies of the following proteins: Nup133, Nup160, Nup96, Nup75, Nup107, Seh1, Sec13, Nup43, Nup37, and ALADIN. Components are arranged in 8-fold symmetrical 'spokes' around the central transport channel. A single 'spoke', can be isolated and is sometimes referred to as the Nup84 complex (S. cerevisiae) or the Nup107-160 complex (vertebrates). |
| nuclear proteasome complex | A proteasome found in the nucleus of a cell. |
| nuclear replication fork | The Y-shaped region of a nuclear replicating DNA molecule, resulting from the separation of the DNA strands and in which the synthesis of new strands takes place. Also includes associated protein complexes. |
| nuclear replisome | A multi-component enzymatic machine at the nuclear replication fork, which mediates DNA replication. Includes DNA primase, one or more DNA polymerases, DNA helicases, and other proteins. |
| nuclear rna export factor complex | A protein complex that contains two proteins (know in several organisms, including Drosophila, as NXF1 and NXF2) and is required for the export of the majority of mRNAs from the nucleus to the cytoplasm; localized in the nucleoplasm and at both the nucleoplasmic and cytoplasmic faces of the nuclear pore complex; shuttles between the nucleus and the cytoplasm. |
| nuclear rna-directed rna polymerase complex | A complex required for RNAi mediated heterochromatin assembly. In S. pombe this contains RNA-directed RNA polymerase, a putative helicase and a protein containing a pap25 associated domain. |
| nuclear speck | A discrete extra-nucleolar subnuclear domain, 20-50 in number, in which splicing factors are seen to be localized by immunofluorescence microscopy. |
| nuclear stress granule | A dense aggregation in the nucleus composed of proteins and RNAs that appear when the cell is under stress. |
| nuclear telomere cap complex | A complex of DNA and protein located at the end of a linear chromosome in the nucleus that protects and stabilizes a linear chromosome. |
| nuclear telomeric heterochromatin | Heterochromatic regions of the chromosome found at the telomeres of a chromosome in the nucleus. |
| nuclear transcription factor complex | A protein complex, located in the nucleus, that is capable of associating with DNA by direct binding, or via other DNA-binding proteins or complexes, and regulating transcription. |
| nuclear transcriptional repressor complex | A protein complex, located in the nucleus, that possesses activity that prevents or downregulates transcription. |
| nuclear ubiquitin ligase complex | A ubiquitin ligase complex found in the nucleus. |
| nucleocytoplasmic shuttling complex | Any complex that acts to move proteins or RNAs into or out of the nucleus through nuclear pores. |
| nucleoid | The region of a virus, bacterial cell, mitochondrion or chloroplast to which the nucleic acid is confined. |
| nucleolar chromatin | The portion of nuclear chromatin associated with the nucleolus; includes the DNA encoding the ribosomal RNA. |
| nucleolar part | Any constituent part of a nucleolus, a small, dense body one or more of which are present in the nucleus of eukaryotic cells. It is rich in RNA and protein, is not bounded by a limiting membrane, and is not seen during mitosis. |
| nucleolar ribonuclease p complex | A ribonuclease P complex located in the nucleolus of a eukaryotic cell, where it catalyzes the 5' endonucleolytic cleavage of precursor tRNAs to yield mature tRNAs. Eukaryotic nucleolar ribonuclease P complexes generally contain a single RNA molecule that is necessary but not sufficient for catalysis, and several protein molecules. |
| nucleolus | A small, dense body one or more of which are present in the nucleus of eukaryotic cells. It is rich in RNA and protein, is not bounded by a limiting membrane, and is not seen during mitosis. Its prime function is the transcription of the nucleolar DNA into 45S ribosomal-precursor RNA, the processing of this RNA into 5.8S, 18S, and 28S components of ribosomal RNA, and the association of these components with 5S RNA and proteins synthesized outside the nucleolus. This association results in the formation of ribonucleoprotein precursors; these pass into the cytoplasm and mature into the 40S and 60S subunits of the ribosome. |
| nucleolus organizer region | A region of a chromosome where nucleoli form during interphase, and where genes encoding the largest rRNA precursor transcript are tandemly arrayed. |
| nucleoplasm | That part of the nuclear content other than the chromosomes or the nucleolus. |
| nucleoplasm part | Any constituent part of the nucleoplasm, that part of the nuclear content other than the chromosomes or the nucleolus. |
| nucleosome | A complex comprised of DNA wound around a multisubunit core and associated proteins, which forms the primary packing unit of DNA into higher order structures. |
| nucleotide-excision repair complex | Any complex formed of proteins that act in nucleotide-excision repair. |
| nucleotide-excision repair factor 1 complex | One of several protein complexes involved in nucleotide-excision repair; possesses DNA damage recognition and endodeoxynuclease activities. In S. cerevisiae, it is composed of Rad1p, Rad10p, and Rad14p; in human the subunits are ERCC4/XPF, ERCC1 and XPA, respectively. |
| nucleus | A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated. In most cells, the nucleus contains all of the cell's chromosomes except the organellar chromosomes, and is the site of RNA synthesis and processing. In some species, or in specialized cell types, RNA metabolism or DNA replication may be absent. |
| nurd complex | An approximately 2 MDa multi-subunit complex that exhibits ATP-dependent chromatin remodeling activity in addition to histone deacetylase (HDAC) activity, and has been shown to establish transcriptional repression of a number of target genes in vertebrates, invertebrates and fungi. Amongst its subunits, the NuRD complex contains histone deacetylases, histone binding proteins and Mi-2-like proteins. |
| nurf complex | An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2L in mammals), a NURF301 homolog (BPTF in humans), and additional subunits, though the composition of these additional subunits varies slightly with species. NURF is involved in regulation of transcription from TRNA polymerase II promoters. |
| occluding junction | A cell-cell junction that seals cells together in an epithelium in a way that prevents even small molecules from leaking from one side of the sheet to the other. |
| oligosaccharyltransferase complex | A protein complex that is found in the endoplasmic reticulum membrane of eukaryotes and transfers lipid-linked oligosaccharide precursor to asparagine residues on nascent proteins. In yeast, the complex includes at least nine different subunits, whereas in mammalian cells at least three different forms of the complex have been detected. |
| oncostatin-m receptor complex | A heterodimeric receptor for the cytokine oncostatin-M (OSM). In humans the receptor complex is made up of the gene products gp130 and OSMR-beta. |
| organellar large ribosomal subunit | The larger of the two subunits of an organellar ribosome. Two sites on the ribosomal large subunit are involved in translation: the aminoacyl site (A site) and peptidyl site (P site). |
| organellar ribosome | A ribosome contained within a subcellular membrane-bounded organelle. |
| organellar small ribosomal subunit | The smaller of the two subunits of an organellar ribosome. |
| organelle | Organized structure of distinctive morphology and function. Includes the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton, and prokaryotic structures such as anammoxosomes and pirellulosomes. Excludes the plasma membrane. |
| organelle envelope | A double membrane structure enclosing an organelle, including two lipid bilayers and the region between them. In some cases, an organelle envelope may have more than two membranes. |
| organelle envelope lumen | The region between the inner and outer lipid bilayers of an organelle envelope. |
| organelle inner membrane | The inner, i.e. lumen-facing, lipid bilayer of an organelle envelope; usually highly selective to most ions and metabolites. |
| organelle lumen | The internal volume enclosed by the membranes of a particular organelle; includes the volume enclosed by a single organelle membrane, e.g. endoplasmic reticulum lumen, or the volume enclosed by the innermost of the two lipid bilayers of an organelle envelope, e.g. nuclear lumen. |
| organelle membrane | A membrane that is one of the two lipid bilayers of an organelle envelope or the outermost membrane of single membrane bound organelle. |
| organelle membrane contact site | A zone of apposition between the membranes of two organelles, structured by bridging complexes. Membrane contact sites (MCSs) are specialized for communication, including the efficient traffic of small molecules such as Ca2+ ions and lipids, as well as enzyme-substrate interactions. |
| organelle outer membrane | The outer, i.e. cytoplasm-facing in a cellular organelle, lipid bilayer of an organelle envelope. |
| organelle part | Any constituent part of an organelle, an organized structure of distinctive morphology and function. Includes constituent parts of the nucleus, mitochondria, plastids, vacuoles, vesicles, ribosomes and the cytoskeleton, but excludes the plasma membrane. |
| organelle subcompartment | A compartment that consists of a lumen and an enclosing membrane, and is part of an organelle. |
| origin recognition complex | A multisubunit complex that is located at the replication origins of a chromosome. |
| other organism | A secondary organism with which the first organism is interacting. |
| other organism cell | A cell of a secondary organism with which the first organism is interacting. |
| other organism cell membrane | The cell membrane of a secondary organism with which the first organism is interacting. |
| other organism membrane | A membrane of a secondary organism with which the first organism is interacting. |
| other organism part | Any constituent part of a secondary organism with which the first organism is interacting. |
| other organism presynaptic membrane | A presynaptic membrane that is part of another organism, i.e. a secondary organism with which the first organism is interacting. A presynaptic membrane is specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane. |
| outer acrosomal membrane | The acrosomal membrane region that underlies the plasma membrane of the sperm. This membrane fuses with the sperm plasma membrane as part of the acrosome reaction. |
| outer dense fiber | Structure or material found in the flagella of mammalian sperm that surrounds each of the nine microtubule doublets, giving a 9 + 9 + 2 arrangement rather than the 9 + 2 pattern usually seen. These dense fibers are stiff and noncontractile. |
| outer dynein arm | Outer arm structure present on the outer doublet microtubules of ciliary and flagellar axonemes. Outer dynein arms contain 2-3 heavy chains, two or more intermediate chains and a cluster of 4-8 light chains. Inner and outer dynein arms have different functions in the generation of microtubule-based motility. |
| outer membrane | The external membrane of Gram-negative bacteria or certain organelles such as mitochondria and chloroplasts; freely permeable to most ions and metabolites. |
| outer mucus layer | The outer of two mucus layers secreted by epithelial cells in the colon; the outer mucus layer is loosely packed and can be colonized by bacteria. |
| oxidoreductase complex | Any protein complex that possesses oxidoreductase activity. |
| oxoglutarate dehydrogenase complex | A complex of multiple copies of three enzymatic components: oxoglutarate dehydrogenase (lipoamide) ; EC:1.2.4.2 (E1), dihydrolipoamide S-succinyltransferase ; EC:2.3.1.61 (E2) and dihydrolipoamide dehydrogenase ; EC:1.8.1.4 (E3); catalyzes the overall conversion of 2-oxoglutarate to succinyl-CoA and carbon dioxide (CO2). |
| p granule | A small cytoplasmic, non-membranous RNA/protein complex aggregates in the primordial germ cells of many higher eukaryotes. |
| palmitoyltransferase complex | A protein complex with palmitoyltransferase activity. |
| pan complex | A complex that possesses poly(A)-specific ribonuclease activity; catalyzes the message-specific shortening of mRNA poly(A) tails. Contains at least two subunits, known as Pan2p and Pan3p in Saccharomyces. |
| paraferritin complex | A cytoplasmic protein complex that contains integrin, mobilferrin and a flavin monooxygenase, is capable of reducing Fe(III) to Fe(II) utilizing NADPH, and is involved in iron transport. Fe(II) is required in the cell as the substrate for ferrochelatase in the synthesis of heme. |
| parallel fiber | A parallel fiber results from the bifurcation of a cerebellar granule cell axon in the molecular layer into two diametrically opposed branches, that are oriented parallel to the long axis of the folium. |
| paranodal junction | A highly specialized cell-cell junction found in vertebrates, which forms between a neuron and a glial cell, and has structural similarity to Drosophila septate junctions. It flanks the node of Ranvier in myelinated nerve and electrically isolates the myelinated from unmyelinated nerve segments and physically separates the voltage-gated sodium channels at the node from the cluster of potassium channels underneath the myelin sheath. |
| paranode region of axon | An axon part that is located adjacent to the nodes of Ranvier and surrounded by lateral loop portions of myelin sheath. |
| paraspeckles | Discrete subnuclear bodies in the interchromatin nucleoplasmic space, often located adjacent to nuclear specks. 10-20 paraspeckles are typically found in human cell nuclei. |
| pas complex | A class III phosphatidylinositol 3-kinase complex that contains a phosphatidylinositol-3-phosphate 5-kinase subunit (Fab1p in yeast; PIKfyve in mammals), a kinase activator, and a phosphatase, and may also contain additional proteins; it is involved in regulating the synthesis and turnover of phosphatidylinositol 3,5-bisphosphate. In mammals the complex is composed of PIKFYVE, FIG4 and VAC14. In yeast it is composed of Atg18p, Fig4p, Fab1p, Vac14p and Vac7p. |
| pcaf complex | A large multiprotein complex that possesses histone acetyltransferase activity and is involved in regulation of transcription. The composition is similar to that of the SAGA complex, but includes fewer Spt and Ada proteins, and more TAFs. |
| pcg protein complex | A chromatin-associated multiprotein complex containing Polycomb Group proteins. In Drosophila, Polycomb group proteins are involved in the long-term maintenance of gene repression, and PcG protein complexes associate with Polycomb group response elements (PREs) in target genes to regulate higher-order chromatin structure. |
| pcna complex | A protein complex composed of three identical PCNA monomers, each comprising two similar domains, which are joined in a head-to-tail arrangement to form a homotrimer. Forms a ring-like structure in solution, with a central hole sufficiently large to accommodate the double helix of DNA. Originally characterized as a DNA sliding clamp for replicative DNA polymerases and as an essential component of the replisome, and has also been shown to be involved in other processes including Okazaki fragment processing, DNA repair, translesion DNA synthesis, DNA methylation, chromatin remodeling and cell cycle regulation. |
| pcna-p21 complex | A protein complex that contains the cyclin-dependent protein kinase inhibitor p21WAF1/CIP1 bound to PCNA; formation of the complex inhibits DNA replication. |
| pebow complex | A protein complex that is involved in coordinating ribosome biogenesis with cell cycle progression. In human, it is composed of Pes1, Bop1, and WDR12; in Saccharomyces the proteins are known as Nop7p, Erb1 and Ytm1 respectively. |
| pentameric igm immunoglobulin complex | A circulating form of IgM consisting of a pentamer of IgM core units with a single J chain polypeptide. |
| pericentric heterochromatin | Heterochromatin that is located adjacent to the CENP-A rich centromere 'central core' and characterized by the modified histone H3K9me3. |
| pericentriolar material | A network of small fibers that surrounds the centrioles in cells; contains the microtubule nucleating activity of the centrosome. |
| perichromatin fibrils | Structures of variable diameter visible in the nucleoplasm by electron microscopy, mainly observed near the border of condensed chromatin. The fibrils are enriched in RNA, and are believed to be sites of pre-mRNA splicing and polyadenylylation representing the in situ form of nascent transcripts. |
| perikaryon | The portion of the cell soma (cell body) that excludes the nucleus. |
| perineuronal net | A dense extracellular matrix (ECM) structure that forms around many neuronal cell bodies and dendrites late in development and is responsible for synaptic stabilization in the adult brain. |
| perinuclear endoplasmic reticulum | The portion of endoplasmic reticulum, the intracellular network of tubules and cisternae, that occurs near the nucleus. The lumen of the perinuclear endoplasmic reticulum is contiguous with the nuclear envelope lumen (also called perinuclear space), the region between the inner and outer nuclear membranes. |
| perinuclear region of cytoplasm | Cytoplasm situated near, or occurring around, the nucleus. |
| perinuclear theca | A condensed cytoplasmic structure that covers the nucleus of mammalian spermatozoa except for a narrow zone around the insertion of the tail. It shows two distinct regions, a subacrosomal layer and, continuing caudally beyond the acrosomic system, the postacrosomal sheath. The perinuclear theca has been considered a cytoskeletal scaffold responsible for maintaining the overall architecture of the mature sperm head; however, recent studies indicate that the bulk of its constituent proteins are not traditional cytoskeletal proteins but rather a variety of cytosolic proteins. |
| perinucleolar chromocenter | A chromocenter adjacent to the nucleolus. |
| peroxisomal matrix | The volume contained within the membranes of a peroxisome; in many cells the matrix contains a crystalloid core largely composed of urate oxidase. |
| peroxisomal membrane | The lipid bilayer surrounding a peroxisome. |
| peroxisomal part | Any constituent part of a peroxisome, a small, membrane-bounded organelle that uses dioxygen (O2) to oxidize organic molecules; contains some enzymes that produce and others that degrade hydrogen peroxide (H2O2). |
| peroxisome | A small organelle enclosed by a single membrane, and found in most eukaryotic cells. Contains peroxidases and other enzymes involved in a variety of metabolic processes including free radical detoxification, lipid catabolism and biosynthesis, and hydrogen peroxide metabolism. |
| phagocytic cup | An invagination of the cell membrane formed by an actin dependent process during phagocytosis. Following internalization it is converted into a phagosome. |
| phagocytic vesicle | A membrane-bounded intracellular vesicle that arises from the ingestion of particulate material by phagocytosis. |
| phagocytic vesicle lumen | The volume enclosed by the membrane of a phagocytic vesicle. |
| phagocytic vesicle membrane | The lipid bilayer surrounding a phagocytic vesicle. |
| phagolysosome | A membrane-bounded intracellular vesicle formed by maturation of an early phagosome following the ingestion of particulate material by phagocytosis; during maturation, phagosomes acquire markers of late endosomes and lysosomes. |
| phagolysosome membrane | The lipid bilayer surrounding a phagolysosome. |
| phosphatase complex | A protein complex which is capable of phosphatase activity. |
| phosphatidylinositol 3-kinase complex | A protein complex capable of phosphatidylinositol 3-kinase activity and containing subunits of any phosphatidylinositol 3-kinase (PI3K) enzyme. These complexes are divided in three classes (called I, II and III) that differ for their presence across taxonomic groups and for the type of their constituents. Catalytic subunits of phosphatidylinositol 3-kinase enzymes are present in all 3 classes; regulatory subunits of phosphatidylinositol 3-kinase enzymes are present in classes I and III; adaptor proteins have been observed in class II complexes and may be present in other classes too. |
| phosphatidylinositol 3-kinase complex, class i | A phosphatidylinositol 3-kinase complex that contains a catalytic and a regulatory subunit of a phosphatidylinositol 3-kinase (PI3K) enzyme, plus one or more adaptor proteins. Class I PI3Ks phosphorylate phosphatidylinositol [PI], phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], and are divided into subclasses A and B according to the type of adaptor subunit with which they associate. The class I PI3K subfamily of genes comprises members in vertebrates, worm and fly, but none in yeast. |
| phosphatidylinositol 3-kinase complex, class ia | A class I phosphatidylinositol 3-kinase complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic class IA phosphoinositide 3-kinase (PI3K) subunit and an associated SH2 domain-containing regulatory subunit that is a member of a family of related proteins often called p85 proteins. Through the interaction with the SH2-containing adaptor subunits, Class IA PI3K catalytic subunits are linked to tyrosine kinase signaling pathways. |
| phosphatidylinositol 3-kinase complex, class ib | A class I phosphatidylinositol 3-kinase complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic class IB phosphoinositide 3-kinase (PI3K) subunit and an associated regulatory subunit that is larger than, and unrelated to, the p85 proteins present in class IA complexes. Class IB PI3Ks are stimulated by G-proteins and do not interact with the SH2-domain containing adaptors that bind to Class IA PI3Ks. |
| phosphatidylinositol 3-kinase complex, class iii | A phosphatidylinositol 3-kinase complex that contains a catalytic class III phosphoinositide 3-kinase (PI3K) subunit bound to a regulatory (adaptor) subunit. Additional adaptor proteins may be present. Class III PI3Ks have a substrate specificity restricted to phosphatidylinositol (PI). |
| phosphopyruvate hydratase complex | A multimeric enzyme complex, usually a dimer or an octamer, that catalyzes the conversion of 2-phospho-D-glycerate to phosphoenolpyruvate and water. |
| phosphorylase kinase complex | An enzyme complex that catalyzes the phosphorylation of phosphorylase b to form phosphorylase a. |
| photoreceptor connecting cilium | A nonmotile primary cilium that has a 9+0 microtubule array and forms the portion of the axoneme traversing the boundary between the photoreceptor inner and outer segments. |
| photoreceptor disc membrane | Ovally-shaped membranous stack located inside the photoreceptor outer segment, and containing densely packed molecules of the photoreceptor protein rhodopsin that traverse the lipid bilayer. Disc membranes are apparently derived from the plasma membrane in the region of the cilium that connects the photoreceptor outer segment to the inner segment. |
| photoreceptor inner segment | The inner segment of a vertebrate photoreceptor containing mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs. |
| photoreceptor inner segment membrane | The membrane surrounding the outer segment of a vertebrate photoreceptor. The photoreceptor inner segment contains mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs. |
| photoreceptor outer segment | The outer segment of a vertebrate photoreceptor that contains discs of photoreceptive membranes. |
| photoreceptor outer segment membrane | The membrane surrounding the outer segment of a vertebrate photoreceptor. |
| pi-body | A P granule that contains the PIWIL2-TDRD1 module, a set of proteins that act in the primary piRNA pathway. The pi-body corresponds to the cementing material between mitochondria found in gonocytes. |
| piccolo nua4 histone acetyltransferase complex | A heterotrimeric H4/H2A histone acetyltransferase complex with a substrate preference of chromatin over free histones. It contains a subset of the proteins found in the larger NuA4 histone acetyltransferase complex; for example, the S. cerevisiae complex contains Esa1p, Yng2p, and Epl1p. |
| picln-sm protein complex | A protein complex that contains pICln (CLNS1A) and several Sm proteins, including SmD1, SmD2, SmE, SmF, and SmG. |
| pigment granule | A small, subcellular membrane-bounded vesicle containing pigment and/or pigment precursor molecules. Pigment granule biogenesis is poorly understood, as pigment granules are derived from multiple sources including the endoplasmic reticulum, coated vesicles, lysosomes, and endosomes. |
| pinosome | A membrane-bounded, uncoated intracellular vesicle formed by the process of pinocytosis. |
| pip-body | A P granule that contains the PIWIL4-TDRD9 module, a set of proteins that act in the secondary piRNA pathway. |
| plasma lipoprotein particle | A spherical particle with a hydrophobic core of triglycerides and/or cholesterol esters, surrounded by an amphipathic monolayer of phospholipids, cholesterol and apolipoproteins. Plasma lipoprotein particles transport lipids, which are non-covalently associated with the particles, in the blood or lymph. |
| plasma membrane | The membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins. |
| plasma membrane part | Any constituent part of the plasma membrane, the membrane surrounding a cell that separates the cell from its external environment. It consists of a phospholipid bilayer and associated proteins. |
| plasma membrane raft | A membrane raft that is part of the plasma membrane. |
| plasma membrane region | A membrane that is a (regional) part of the plasma membrane. |
| platelet alpha granule | A secretory organelle found in blood platelets, which is unique in that it exhibits further compartmentalization and acquires its protein content via two distinct mechanisms: (1) biosynthesis predominantly at the megakaryocyte (MK) level (with some vestigial platelet synthesis) (e.g. platelet factor 4) and (2) endocytosis and pinocytosis at both the MK and circulating platelet levels (e.g. fibrinogen (Fg) and IgG). |
| platelet alpha granule lumen | The volume enclosed by the membrane of the platelet alpha granule. |
| platelet alpha granule membrane | The lipid bilayer surrounding the platelet alpha granule. |
| platelet dense granule | Electron-dense granule occurring in blood platelets that stores and secretes adenosine nucleotides and serotonin. They contain a highly condensed core consisting of serotonin, histamine, calcium, magnesium, ATP, ADP, pyrophosphate and membrane lysosomal proteins. |
| platelet dense granule membrane | The lipid bilayer surrounding the platelet dense granule. |
| platelet dense tubular network | A network of membrane-bounded compartments found in blood platelets, where they regulate platelet activation by sequestering or releasing calcium. The dense tubular network exists as thin elongated membranes in resting platelets, and undergoes a major ultrastructural change, to a rounded vesicular form, upon addition of thrombin. |
| platelet dense tubular network membrane | The lipid bilayer surrounding the platelet dense tubular network. |
| plus-end kinesin complex | Any complex that includes a dimer of molecules from the kinesin superfamily and any associated proteins, and moves towards the plus end of a microtubule. |
| pml body | A class of nuclear body; they react against SP100 auto-antibodies (PML, promyelocytic leukemia); cells typically contain 10-30 PML bodies per nucleus; alterations in the localization of PML bodies occurs after viral infection. |
| podosome | An actin-rich adhesion structure characterized by formation upon cell substrate contact and localization at the substrate-attached part of the cell, contain an F-actin-rich core surrounded by a ring structure containing proteins such as vinculin and talin, and have a diameter of 0.5 mm. |
| polar microtubule | Any of the spindle microtubules that come from each pole and overlap at the spindle midzone. This interdigitating structure consisting of antiparallel microtubules is responsible for pushing the poles of the spindle apart. |
| pole plasm | Differentiated cytoplasm associated with a pole (animal, vegetal, anterior, or posterior) of an oocyte, egg or early embryo. |
| polycystin complex | A stable heterodimeric complex composed of polycystin-1 and polycystin-2. |
| polymeric iga immunoglobulin complex | A protein complex composed of two, three, or four monomeric IgA immunoglobulin complexes linked through both direct disulfide bonds and through disulfide binded monomers of J chain acting as a bridge. Each IgA monomer consists of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds. Dimeric IgA is sometimes complexed additionally with secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. |
| polysomal ribosome | A ribosome bound to mRNA that forms part of a polysome. |
| polysome | A multiribosomal structure representing a linear array of ribosomes held together by messenger RNA. They represent the active complexes in cellular protein synthesis and are able to incorporate amino acids into polypeptides both in vivo and in vitro. |
| pore complex | Any small opening in a membrane that allows the passage of gases and/or liquids. |
| positive transcription elongation factor complex b | A transcription elongation factor complex that facilitates the transition from abortive to productive elongation by phosphorylating the CTD domain of the large subunit of DNA-directed RNA polymerase II, holoenzyme. Contains cyclin T and a cyclin-dependent protein kinase catalytic subunit. |
| post-mrna release spliceosomal complex | A spliceosomal complex that is formed following the release of the spliced product from the post-spliceosomal complex and contains the excised intron and three snRNPs, including U5. |
| postsynaptic density | The postsynaptic density is a region that lies adjacent to the cytoplasmic face of the postsynaptic membrane at excitatory synapse. It forms a disc that consists of a range of proteins with different functions, some of which contact the cytoplasmic domains of ion channels in the postsynaptic membrane. The proteins making up the disc include receptors, and structural proteins linked to the actin cytoskeleton. They also include signalling machinery, such as protein kinases and phosphatases. The postsynaptic density may be part of a neuron or a muscle cell or a glial cell. |
| postsynaptic membrane | A specialized area of membrane facing the presynaptic membrane on the tip of the nerve ending and separated from it by a minute cleft (the synaptic cleft). Neurotransmitters across the synaptic cleft and transmit the signal to the postsynaptic membrane. |
| potassium channel complex | An ion channel complex through which potassium ions pass. |
| pr-dub complex | A multimeric protein complex that removes monoubiquitin from histone H2A. In Drosophila and mammals, the core of the complex is composed of Calypso/BAP1 and Asx/ASXL1, respectively. |
| prc1 complex | A multiprotein complex that mediates monoubiquitination of lysine residues of histone H2A (lysine-118 in Drosophila or lysine-119 in mammals). The complex is required for stable long-term maintenance of transcriptionally repressed states and is involved in chromatin remodeling. |
| pre-autophagosomal structure | A punctate structure localized in the vicinity of the vacuole that is required for the formation of autophagosomes. |
| pre-autophagosomal structure membrane | A cellular membrane associated with the pre-autophagosomal structure. |
| pre-snornp complex | A ribonucleoprotein complex that contains a precursor small nucleolar RNA (pre-snoRNA) and associated proteins, and forms during small nucleolar ribonucleoprotein complex (snoRNP) assembly. Pre-snoRNP complexes may contain proteins not found in the corresponding mature snoRNP complexes. |
| prefoldin complex | A multisubunit chaperone that is capable of delivering unfolded proteins to cytosolic chaperonin, which it acts as a cofactor for. In humans, the complex is a heterohexamer of two PFD-alpha and four PFD-beta type subunits. In Saccharomyces cerevisiae, it also acts in the nucleus to regulate the rate of elongation by RNA polymerase II via a direct effect on histone dynamics. |
| preribosome | Any complex of pre-rRNAs, ribosomal proteins, and associated proteins formed during ribosome biogenesis. |
| preribosome, large subunit precursor | A preribosomal complex consisting of 27SA, 27SB, and/or 7S pre-rRNA, 5S rRNA, ribosomal proteins including late-associating large subunit proteins, and associated proteins; a precursor of the eukaryotic cytoplasmic large ribosomal subunit. |
| preribosome, small subunit precursor | A preribosomal complex consisting of 20S pre-rRNA, ribosomal proteins including late-associating small subunit proteins, and associated proteins; a precursor of the eukaryotic cytoplasmic small ribosomal subunit. |
| prespliceosome | A spliceosomal complex that is formed by association of the 5' splice site and the branch point sequence with specific snRNPs. The prespliceosome includes many proteins in addition to those found in the bound snRNPs. Commitment to a given pair of 5' and 3' splice sites occurs at the time of prespliceosome formation. Prespliceosome complexes are not active for splicing, but are instead an early step in the assembly of a spliceosomal complex. |
| presynaptic active zone | A specialized region of the plasma membrane and cell cortex of a presynaptic neuron; encompasses a region of the plasma membrane where synaptic vesicles dock and fuse, synaptic vesicles, and a specialized cortical cytoskeletal matrix. |
| presynaptic active zone membrane | The membrane portion of the presynaptic active zone; it is the site where docking and fusion of synaptic vesicles occurs for the release of neurotransmitters. |
| presynaptic cytoskeletal matrix assembled at active zones | The specialized cytoskeletal matrix assembled at the active zones of the presynaptic nerve terminal. The cytoskeletal matrix is a proteinaceous structure involved in organizing synaptic events such as immobilisation or translocation of synaptic vesicles, and assembling active zone components. The cytomatrix protein exclusively assembled at active zones, is thought to form a molecular scaffold that organizes neurotransmitter release sites. |
| presynaptic membrane | A specialized area of membrane of the axon terminal that faces the plasma membrane of the neuron or muscle fiber with which the axon terminal establishes a synaptic junction; many synaptic junctions exhibit structural presynaptic characteristics, such as conical, electron-dense internal protrusions, that distinguish it from the remainder of the axon plasma membrane. |
| primary cilium | A cilium found on many different cell types that is typically present in a single copy per cell. A primary cilium may have a variable array of axonemal microtubules and may or may not contain molecular motors. |
| primary lysosome | A lysosome before it has fused with a vesicle or vacuole. |
| procollagen-proline 4-dioxygenase complex | A protein complex that catalyzes the formation of procollagen trans-4-hydroxy-L-proline and succinate from procollagen L-proline and 2-oxoglutarate, requiring Fe2+ and ascorbate. Contains two alpha subunits that contribute to most parts of the catalytic sites, and two beta subunits that are identical to protein-disulfide isomerase. |
| prominosome | An extracellular membrane-bounded vesicle that contains prominin proteins (in mouse Prom1/CD33 or Prom2) and are found in body fluids including ventricular fluid, saliva, urine and seminal fluid. In the ventricular fluid of the developing mouse brain two major classes of these particles have been observed (P2 particles of 500-1000 nm and P4 particles of 50-80 nm) which likely originate from microvilli, primary cilia and/or the midbody of neuroepithelial cells. The physiological role is not known. |
| pronucleus | The nucleus of either the ovum or the spermatozoon following fertilization. Thus, in the fertilized ovum, there are two pronuclei, one originating from the ovum, the other from the spermatozoon that brought about fertilization; they approach each other, but do not fuse until just before the first cleavage, when each pronucleus loses its membrane to release its contents. |
| protease inhibitor complex | A heterodimeric protein complex that contains a protease inhibitor and a protease; formation of the complex inhibits protease activity. |
| proteasome accessory complex | A protein complex, that caps one or both ends of the proteasome core complex and regulates entry into, or exit from, the proteasome core complex. |
| proteasome activator complex | A multisubunit complex that activates the hydrolysis of small nonubiquitinated peptides by binding to the proteasome core complex. |
| proteasome complex | A large multisubunit complex which catalyzes protein degradation, found in eukaryotes, archaea and some bacteria. In eukaryotes, this complex consists of the barrel shaped proteasome core complex and one or two associated proteins or complexes that act in regulating entry into or exit from the core. |
| proteasome core complex | A multisubunit barrel shaped endoprotease complex, which is the core of the proteasome complex. |
| proteasome core complex, alpha-subunit complex | The proteasome core subcomplex that constitutes the two outer rings of the proteasome core complex. An example of this component is found in Mus musculus. |
| proteasome regulatory particle | A multisubunit complex, which caps one or both ends of the proteasome core complex. This complex recognizes and unfolds ubiquitinated proteins, and translocates them to the proteasome core complex. |
| proteasome regulatory particle, base subcomplex | The subcomplex of the proteasome regulatory particle that directly associates with the proteasome core complex. |
| proteasome regulatory particle, lid subcomplex | The subcomplex of the proteasome regulatory particle that forms the peripheral lid, which is added on top of the base subcomplex. |
| protein acetyltransferase complex | A complex that catalyzes the transfer of an acetyl group to a protein acceptor molecule. |
| protein c inhibitor-coagulation factor v complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and coagulation factor V (F5); formation of the complex inhibits the serine protease activity of coagulation factor V. |
| protein c inhibitor-coagulation factor xa complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and coagulation factor Xa (F10); formation of the complex inhibits the serine protease activity of coagulation factor Xa. |
| protein c inhibitor-coagulation factor xi complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and coagulation factor XI (F11); formation of the complex inhibits the serine protease activity of coagulation factor XI. |
| protein c inhibitor-klk3 complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and prostate-specific antigen (KLK3); formation of the complex inhibits the serine protease activity of prostate-specific antigen. |
| protein c inhibitor-plasma kallikrein complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and plasma kallikrein (KLK1B); formation of the complex inhibits the serine protease activity of plasma kallikrein. |
| protein c inhibitor-plat complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and tissue-type plasminogen activator (PLAT); formation of the complex inhibits the serine protease activity of tissue-type plasminogen activator. |
| protein c inhibitor-plau complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and urokinase-type plasminogen activator (PLAU); formation of the complex inhibits the serine protease activity of urokinase-type plasminogen activator. |
| protein c inhibitor-thrombin complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and thrombin (F2); formation of the complex inhibits the serine protease activity of thrombin. |
| protein c inhibitor-tmprss11e complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and transmembrane protease serine 11E (TMPRSS11E); formation of the complex inhibits the serine protease activity of transmembrane protease serine 11E. |
| protein c inhibitor-tmprss7 complex | A heterodimeric protein complex that contains protein C inhibitor (SERPINA5) and transmembrane protease serine 7 (TMPRSS7); formation of the complex inhibits the serine protease activity of transmembrane protease serine 7. |
| protein complex | Any macromolecular complex composed (only) of two or more polypeptide subunits along with any covalently attached molecules (such as lipid anchors or oligosaccharide) or non-protein prosthetic groups (such as nucleotides or metal ions). Prosthetic group in this context refers to a tightly bound cofactor. The component polypeptide subunits may be identical. |
| protein complex involved in cell adhesion | Any protein complex that is capable of carrying out some part of the process of cell-cell adhesion. |
| protein farnesyltransferase complex | A protein complex that possesses protein farnesyltransferase activity. |
| protein kinase ck2 complex | A protein complex that possesses protein serine/threonine kinase activity, and contains two catalytic alpha subunits and two regulatory beta subunits. Protein kinase CK2 complexes are found in nearly every subcellular compartment, and can phosphorylate many protein substrates in addition to casein. |
| protein kinase complex | A protein complex which is capable of protein kinase activity. |
| protein phosphatase 4 complex | The complex formed by the catalytic subunit of protein phosphatase 4 plus a regulatory subunit. |
| protein phosphatase type 1 complex | A protein complex that possesses magnesium-dependent protein serine/threonine phosphatase (AMD phosphatase) activity, and consists of a catalytic subunit and one or more regulatory subunits that dictates the phosphatase's substrate specificity, function, and activity. |
| protein phosphatase type 2a complex | A protein complex that has protein serine/threonine phosphatase activity that is polycation-stimulated (PCS), being directly stimulated by protamine, polylysine, or histone H1; it constitutes a subclass of several enzymes activated by different histones and polylysine, and consists of catalytic, scaffolding, and regulatory subunits. The catalytic and scaffolding subunits form the core enzyme, and the holoenzyme also includes the regulatory subunit. |
| protein serine/threonine phosphatase complex | A complex, normally consisting of a catalytic and a regulatory subunit, which catalyzes the removal of a phosphate group from a serine or threonine residue of a protein. |
| protein-dna complex | A macromolecular complex containing both protein and DNA molecules. |
| protein-lipid complex | A macromolecular complex containing separate protein and lipid molecules. Separate in this context means not covalently bound to each other. |
| proteinaceous extracellular matrix | A layer consisting mainly of proteins (especially collagen) and glycosaminoglycans (mostly as proteoglycans) that forms a sheet underlying or overlying cells such as endothelial and epithelial cells. The proteins are secreted by cells in the vicinity. An example of this component is found in Mus musculus. |
| proton-transporting atp synthase complex | A proton-transporting two-sector ATPase complex that catalyzes the phosphorylation of ADP to ATP during oxidative phosphorylation. The complex comprises a membrane sector (F0) that carries out proton transport and a cytoplasmic compartment sector (F1) that catalyzes ATP synthesis by a rotational mechanism; the extramembrane sector (containing 3 a and 3 b subunits) is connected via the d-subunit to the membrane sector by several smaller subunits. Within this complex, the g and e subunits and the 9-12 c subunits rotate by consecutive 120 degree angles and perform parts of ATP synthesis. This movement is driven by the hydrogen ion electrochemical potential gradient. |
| proton-transporting atp synthase complex, catalytic core f(1) | The sector of a hydrogen-transporting ATP synthase complex in which the catalytic activity resides; it comprises the catalytic core and central stalk, and is peripherally associated with a membrane, such as the plasma membrane or the mitochondrial inner membrane, when the entire ATP synthase is assembled. |
| proton-transporting atp synthase complex, coupling factor f(o) | All non-F1 subunits of a hydrogen-transporting ATP synthase, including integral and peripheral membrane proteins. |
| proton-transporting atp synthase, catalytic core | The hexamer that possesses the catalytic activity of the mitochondrial hydrogen-transporting ATP synthase. |
| proton-transporting two-sector atpase complex | A large protein complex that catalyzes the synthesis or hydrolysis of ATP by a rotational mechanism, coupled to the transport of protons across a membrane. The complex comprises a membrane sector (F0, V0, or A0) that carries out proton transport and a cytoplasmic compartment sector (F1, V1, or A1) that catalyzes ATP synthesis or hydrolysis. Two major types have been characterized: V-type ATPases couple ATP hydrolysis to the transport of protons across a concentration gradient, whereas F-type ATPases, also known as ATP synthases, normally run in the reverse direction to utilize energy from a proton concentration or electrochemical gradient to synthesize ATP. A third type, A-type ATPases have been found in archaea, and are closely related to eukaryotic V-type ATPases but are reversible. |
| proton-transporting two-sector atpase complex, catalytic domain | A protein complex that forms part of a proton-transporting two-sector ATPase complex and catalyzes ATP hydrolysis or synthesis. The catalytic domain (F1, V1, or A1) comprises a hexameric catalytic core and a central stalk, and is peripherally associated with the membrane when the two-sector ATPase is assembled. |
| proton-transporting two-sector atpase complex, proton-transporting domain | A protein complex that forms part of a proton-transporting two-sector ATPase complex and carries out proton transport across a membrane. The proton-transporting domain (F0, V0, or A0) includes integral and peripheral membrane proteins. |
| proton-transporting v-type atpase complex | A proton-transporting two-sector ATPase complex that couples ATP hydrolysis to the transport of protons across a concentration gradient. The resulting transmembrane electrochemical potential of H+ is used to drive a variety of (i) secondary active transport systems via H+-dependent symporters and antiporters and (ii) channel-mediated transport systems. The complex comprises a membrane sector (V0) that carries out proton transport and a cytoplasmic compartment sector (V1) that catalyzes ATP hydrolysis. V-type ATPases are found in the membranes of organelles such as vacuoles, endosomes, and lysosomes, and in the plasma membrane. |
| proton-transporting v-type atpase, v0 domain | A protein complex that forms part of a proton-transporting V-type ATPase and mediates proton transport across a membrane. The V0 complex consists of at least four different subunits (a,c,d and e); six or more c subunits form a proton-binding rotor ring. |
| proton-transporting v-type atpase, v1 domain | A protein complex that forms part of a proton-transporting V-type ATPase and catalyzes ATP hydrolysis. The V1 complex consists of: (1) a globular headpiece with three alternating copies of subunits A and B that form a ring, (2) a central rotational stalk composed of single copies of subunits D and F, and (3) a peripheral stalk made of subunits C, E, G and H. Subunits A and B mediate the hydrolysis of ATP at three reaction sites associated with subunit A. |
| prp19 complex | A protein complex consisting of Prp19 and associated proteins that is involved in the transition from the precatalytic spliceosome to the activated form that catalyzes step 1 of splicing, and which remains associated with the spliceosome through the second catalytic step. It is widely conserved, found in both yeast and mammals, though the exact composition varies. In S. cerevisiae, it contains Prp19p, Ntc20p, Snt309p, Isy1p, Syf2p, Cwc2p, Prp46p, Clf1p, Cef1p, and Syf1p. |
| pseudopodium | A temporary cytoplasmic extrusion by means of which an ameba or other ameboid organism or cell moves about or engulfs food. |
| pseudopodium membrane | The portion of the plasma membrane surrounding a pseudopodium. |
| ptw/pp1 phosphatase complex | A protein serine/threonine phosphatase complex that contains a catalytic subunit (PPP1CA, PPP1CB or PPP1CC) and the regulatory subunits PPP1R10 (PNUTS), TOX4 and WDR82, and plays a role in the control of chromatin structure and cell cycle progression during the transition from mitosis into interphase. |
| pyruvate dehydrogenase complex | Complex that carries out the oxidative decarboxylation of pyruvate to form acetyl-CoA; comprises subunits possessing three catalytic activities: pyruvate dehydrogenase (E1), dihydrolipoamide S-acetyltransferase (E2), and dihydrolipoamide dehydrogenase (E3). |
| rab-protein geranylgeranyltransferase complex | A heterodimeric enzyme complex, which in mammals is composed of an alpha and a beta subunit, and which associates with an accessory protein Rep (Rab escort protein). Catalyzes of the transfer of a geranyl-geranyl group from geranylgeranyl pyrophosphate to a Rab protein. |
| rad51b-rad51c-rad51d-xrcc2 complex | A DNA recombinase mediator complex that contains the Rad51 paralogs RAD51B, RAD51C, RAD51D, and XRCC2, or orthologs thereof. |
| rad51c-xrcc3 complex | A DNA recombinase mediator complex that contains the Rad51 paralogs RAD51C and XRCC3, or orthologs thereof. |
| radial spoke | Protein complex that links the outer microtubule doublet of the ciliary or flagellum axoneme with the sheath that surrounds the central pair of microtubules. Composed of a stalk that attaches to each doublet microtubule and a globular structure (spoke head) that projects toward the central pair of microtubules. |
| ragulator complex | A protein complex that contains MAPKSP1 (MP1, Map2k1ip1), ROBLD3 (p14, Mapbpip), and C11orf59 (p18). The complex is anchored to lipid rafts in late endosome membranes via C11orf59, recruits mTORC1 to lysosomal membranes in amino acid signaling to mTORC1, and is also involved in ERK/MAPK signaling. |
| rb-e2f complex | A multiprotein complex containing a heterodimeric E2F transcription factor and a Retinoblastoma (Rb) family member. This complex is capable of repressing transcription of E2F-regulated genes in order to regulate cell cycle progression. |
| rdna heterochromatin | A region of heterochromatin located at the rDNA repeats in a chromosome. |
| receptor complex | Any protein complex that undergoes combination with a hormone, neurotransmitter, drug or intracellular messenger to initiate a change in cell function. |
| recycling endosome | Organelle consisting of networks of 60nm tubules organized around the microtubule organizing centre in some cell types. They transport molecules (e.g., receptors, transporters, lipids) derived from endosomes, the Golgi apparatus, or the cytoplasm to the plasma membrane. Transported molecules may be recycled for reuse, or may be newly synthesized. |
| recycling endosome membrane | The lipid bilayer surrounding a recycling endosome. |
| replication fork | The Y-shaped region of a replicating DNA molecule, resulting from the separation of the DNA strands and in which the synthesis of new strands takes place. Also includes associated protein complexes. |
| replication fork protection complex | A protein complex conserved in eukaryotes and associated with the replication fork; the complex stabilizes stalled replication forks and is thought to be involved in coordinating leading- and lagging-strand synthesis and in replication checkpoint signaling. |
| replisome | A multi-component enzymatic machine at the replication fork which mediates DNA replication. Includes DNA primase, one or more DNA polymerases, DNA helicases, and other proteins. |
| res complex | A protein complex that is required for efficient splicing, and prevents leakage of unspliced pre-mRNAs from the nucleus (named for pre-mRNA REtention and Splicing). In Saccharomyces, the complex consists of Ist3p, Bud13p, and Pml1p. |
| respiratory chain | The protein complexes that form the electron transport system (the respiratory chain), associated with a cell membrane, usually the plasma membrane (in prokaryotes) or the inner mitochondrial membrane (on eukaryotes). The respiratory chain complexes transfer electrons from an electron donor to an electron acceptor and are associated with a proton pump to create a transmembrane electrochemical gradient. |
| respiratory chain complex i | Respiratory chain complex I is an enzyme of the respiratory chain. It consists of several polypeptide chains and is L-shaped, with a horizontal arm lying in the membrane and a vertical arm that projects into the matrix. The electrons of NADH enter the chain at this complex. |
| respiratory chain complex ii | A part of the respiratory chain, containing the four polypeptide subunits of succinate dehydrogenase, flavin-adenine dinucleotide and iron-sulfur. Catalyzes the oxidation of succinate by ubiquinone. Connects the TCA cycle with the respiratory chain. |
| respiratory chain complex iii | A protein complex that transfers electrons from ubiquinol to cytochrome c and translocates two protons across a membrane. The complex contains a core structure of three catalytic subunits: cytochrome b, the Rieske iron sulfur protein (ISP), and cytochrome c1, which are arranged in an integral membrane-bound dimeric complex; additional subunits are present, and vary among different species. |
| respiratory chain complex iv | A part of the respiratory chain, containing the 13 polypeptide subunits of cytochrome c oxidase, including cytochrome a and cytochrome a3. Catalyzes the oxidation of reduced cytochrome c by dioxygen (O2). |
| retromer complex | A conserved multimeric membrane-associated complex involved in retrograde transport from endosomes to the Golgi apparatus. For example, the budding yeast retromer comprises Vps35p, Vps29p, Vps26p, Vps5p, and Vps17p. |
| rhabdomere | The specialized microvilli-containing organelle on the apical surfaces of a photoreceptor cell containing the visual pigment rhodopsin and most of the proteins involved in phototransduction. |
| ribonuclease h2 complex | A protein complex that possesses ribonuclease H activity, in which the catalytic subunit is a member of the RNase H2 (or HII) class. For example, in Saccharomyces the complex contains Rnh201p, Rnh202p and Rnh203p. |
| ribonuclease mrp complex | A ribonucleoprotein complex that contains an RNA molecule of the snoRNA family, and cleaves the rRNA precursor as part of rRNA transcript processing. It also has other roles: In S. cerevisiae it is involved in cell cycle-regulated degradation of daughter cell-specific mRNAs, while in mammalian cells it also enters the mitochondria and processes RNAs to create RNA primers for DNA replication. |
| ribonuclease p complex | A ribonucleoprotein complex that catalyzes cleavage of the leader sequence of precursor tRNAs (pre-tRNAs), generating the mature 5' end of tRNAs. |
| ribonucleoprotein complex | A macromolecular complex containing both protein and RNA molecules. |
| ribonucleoprotein granule | A non-membranous macromolecular complex containing proteins and translationally silenced mRNAs. RNA granules contain proteins that control the localization, stability, and translation of their RNA cargo. Different types of RNA granules (RGs) exist, depending on the cell type and cellular conditions. |
| ribose phosphate diphosphokinase complex | A protein complex having ribose phosphate diphosphokinase activity. |
| ribosomal subunit | Either of the two subunits of a ribosome: the ribosomal large subunit or the ribosomal small subunit. |
| ribosome | An intracellular organelle, about 200 A in diameter, consisting of RNA and protein. It is the site of protein biosynthesis resulting from translation of messenger RNA (mRNA). It consists of two subunits, one large and one small, each containing only protein and RNA. Both the ribosome and its subunits are characterized by their sedimentation coefficients, expressed in Svedberg units (symbol: S). Hence, the prokaryotic ribosome (70S) comprises a large (50S) subunit and a small (30S) subunit, while the eukaryotic ribosome (80S) comprises a large (60S) subunit and a small (40S) subunit. Two sites on the ribosomal large subunit are involved in translation, namely the aminoacyl site (A site) and peptidyl site (P site). Ribosomes from prokaryotes, eukaryotes, mitochondria, and chloroplasts have characteristically distinct ribosomal proteins. |
| ric1-rgp1 guanyl-nucleotide exchange factor complex | A protein complex that acts as a nucleotide exchange factor for the GTPase Ypt6p, and is required for fusion of endosome-derived vesicles with the Golgi. |
| ripoptosome | A protein complex whose core components are the receptor-interacting serine/threonine-protein kinases RIPK1 and RIPK3 (also called RIP1 and RIP3). Formation of the ripoptosome can induce an extrinsic apoptotic signaling pathway or a necroptotic signaling pathway. The composition of this protein complex may depend on several factors including nature of the signal, cell type and more. |
| risc complex | A ribonucleoprotein complex that contains members of the Argonaute family of proteins, small interfering RNAs (siRNAs) or microRNAs (miRNAs), and miRNA or siRNA-complementary mRNAs, in addition to a number of accessory factors. The RISC complex is involved in posttranscriptional repression of gene expression through downregulation of translation or induction of mRNA degradation. |
| rna cap binding complex | Any protein complex that binds to a specialized RNA cap structure at any time in the lifetime of the RNA. |
| rna polymerase complex | Any complex that possesses RNA polymerase activity; generally comprises a catalytic subunit and one or more additional subunits. |
| rna polymerase i core factor complex | A RNA polymerase I-specific transcription factor complex that is required for the transcription of rDNA by RNA polymerase I. In yeast the complex consists of Rrn6p, Rrn7p, and Rrn11p. |
| rna polymerase i transcription factor complex | A transcription factor complex that acts at promoters of genes transcribed by RNA polymerase I. |
| rna polymerase ii transcription factor complex | A transcription factor complex that acts at promoters of genes transcribed by RNA polymerase II. |
| rna polymerase ii transcription repressor complex | A protein complex, located in the nucleus, that possesses activity that prevents or downregulates transcription from a RNA polymerase II promoter. |
| rna polymerase iii transcription factor complex | A transcription factor complex that acts at promoters of genes transcribed by RNA polymerase III. |
| rna-directed rna polymerase complex | A protein complex that possesses RNA-directed RNA polymerase activity. |
| rnai effector complex | Any protein complex that mediates the effects of small interfering RNAs on gene expression. Most known examples contain one or more members of the Argonaute family of proteins. |
| rough endoplasmic reticulum | The rough (or granular) endoplasmic reticulum (ER) has ribosomes adhering to the outer surface; the ribosomes are the site of translation of the mRNA for those proteins which are either to be retained within the cisternae (ER-resident proteins), the proteins of the lysosomes, or the proteins destined for export from the cell. Glycoproteins undergo their initial glycosylation within the cisternae. |
| rough endoplasmic reticulum lumen | The volume enclosed by the membranes of the rough endoplasmic reticulum. |
| rough endoplasmic reticulum membrane | The lipid bilayer surrounding the rough endoplasmic reticulum. |
| rsf complex | An ISWI complex that contains an ATPase subunit of the ISWI family (SNF2H in mammals) and an RSF1 homolog. It mediates nucleosome deposition and generates regularly spaced nucleosome arrays. In mammals, RSF is involved in regulation of transcription from RNA polymerase II promoters). |
| ruffle | Projection at the leading edge of a crawling cell; the protrusions are supported by a microfilament meshwork. |
| ruffle membrane | The portion of the plasma membrane surrounding a ruffle. |
| saga complex | A SAGA-type histone acetyltransferase complex that contains Spt8 (in budding yeast) or a homolog thereof; additional polypeptides include Spt group, consisting of Spt7, Spt3, and Spt20/Ada5, which interact with the TATA-binding protein (TBP); the Ada group, consisting of Ada1, Ada2, Ada3, Ada4/Gcn5, and Ada5/Spt20, which is functionally linked to the nucleosomal HAT activity; Tra1, an ATM/PI-3 kinase-related protein that targets DNA-bound activators for recruitment to promoters; the TBP-associated factor (TAF) proteins, consisting of Taf5, Taf6, Taf9, Taf10, and Taf12, which mediate nucleosomal HAT activity and are thought to help recruit the basal transcription machinery. |
| saga-type complex | A histone acetyltransferase complex that acetylates nucleosomal H3 and H2B and is required for the expression of a subset of Pol II-transcribed genes. The budding yeast complex includes the acetyltransferase Gcn5p, several proteins of the Spt and Ada families, and several TBP-associate proteins (TAFs); analogous complexes in other species have analogous compositions, and usually contain homologs of the yeast proteins. |
| sarcoglycan complex | A protein complex formed of four sarcoglycans plus sarcospan; there are six known sarcoglycans: alpha-, beta-, gamma-, delta-, epsilon- and zeta-sarcoglycan; all are N-glycosylated single-pass transmembrane proteins. The sarcoglycan-sarcospan complex is a subcomplex of the dystrophin glycoprotein complex, and is fixed to the dystrophin axis by a lateral association with the dystroglycan complex. |
| sarcolemma | The outer membrane of a muscle cell, consisting of the plasma membrane, a covering basement membrane (about 100 nm thick and sometimes common to more than one fiber), and the associated loose network of collagen fibers. |
| sarcomere | The repeating unit of a myofibril in a muscle cell, composed of an array of overlapping thick and thin filaments between two adjacent Z discs. |
| sarcoplasm | The cytoplasm of a muscle cell; includes the sarcoplasmic reticulum. |
| sarcoplasmic reticulum | A fine reticular network of membrane-limited elements that pervades the sarcoplasm of a muscle cell; continuous over large portions of the cell and with the nuclear envelope; that part of the endoplasmic reticulum specialized for calcium release, uptake and storage. |
| sarcoplasmic reticulum lumen | The volume enclosed by the membranes of the sarcoplasmic reticulum. |
| sarcoplasmic reticulum membrane | The lipid bilayer surrounding the sarcoplasmic reticulum. |
| scar complex | A heterotetrameric complex that includes orthologues of human PIR121, Nap125 and HSPC300 and regulates actin polymerization and/or depolymerization through small GTPase mediated signal transduction. |
| scf ubiquitin ligase complex | A ubiquitin ligase complex in which a cullin from the Cul1 subfamily and a RING domain protein form the catalytic core; substrate specificity is conferred by a Skp1 adaptor and an F-box protein. SCF complexes are involved in targeting proteins for degradation by the proteasome. The best characterized complexes are those from yeast and mammals (with core subunits named Cdc53/Cul1, Rbx1/Hrt1/Roc1). |
| schmidt-lanterman incisure | Regions within compact myelin in which the cytoplasmic faces of the enveloping myelin sheath are not tightly juxtaposed, and include cytoplasm from the cell responsible for making the myelin. Schmidt-Lanterman incisures occur in the compact myelin internode, while lateral loops are analogous structures found in the paranodal region adjacent to the nodes of Ranvier. |
| schwann cell microvillus | Small finger-like extension of a Schwann cell that contacts the nodal membrane. |
| scrib-apc-beta-catenin complex | A protein complex that contains the Scribble protein (a cell polarity determinant), the tumor suppressor protein adenomatous polyposis coli (APC), and beta-catenin; may be involved in the control of cell proliferation. |
| sec61 translocon complex | A translocon complex that contains a core heterotrimer of conserved alpha, beta and gamma subunits, and may contain additional proteins (translocon-associated proteins or TRAPs); in budding yeast the core proteins are Sec61p, Sbh1p, and Sss1p. The Sec61 translocon complex functions in cotranslational and posttranslational translocation events. |
| secondary lysosome | Vacuole formed by the fusion of a lysosome with an organelle (autosome) or with a primary phagosome. |
| secretory dimeric iga immunoglobulin complex | A dimeric form of secretory IgA immunoglobulin complex. |
| secretory granule | A small subcellular vesicle, surrounded by a membrane, that is formed from the Golgi apparatus and contains a highly concentrated protein destined for secretion. Secretory granules move towards the periphery of the cell and upon stimulation, their membranes fuse with the cell membrane, and their protein load is exteriorized. Processing of the contained protein may take place in secretory granules. |
| secretory granule lumen | The volume enclosed by the membrane of a secretory granule. |
| secretory granule membrane | The lipid bilayer surrounding a secretory granule. |
| secretory iga immunoglobulin complex | A polymeric IgA immunoglobulin complex that is complexed with one chain of secretory component (SC). Polymeric IgA is present in mucosal areas, having been transported via a transcytosis mechanism in mucosal epithelial cells relying on the polymeric Ig receptor, a portion of which then remains bound to the polymeric IgA as secretory component. |
| semaphorin receptor complex | A stable binary complex of a neurophilin and a plexin, together forming a functional semaphorin receptor. |
| senescence-associated heterochromatin focus | A transcriptionally-silent heterochromatin structure present in senescent cells. Contains the condensed chromatin of one chromosome and is enriched for histone modifications. Thought to repress expression of proliferation-promoting genes. |
| septin complex | A protein complex containing septins. Typically, these complexes contain multiple septins and are oligomeric. |
| septin cytoskeleton | The part of the cytoskeleton (the internal framework of a cell) composed of septins and associated proteins. Includes septin cytoskeleton-associated complexes. |
| serine c-palmitoyltransferase complex | An enzyme complex that catalyzes the transfer of a palmitoyl on to serine, forming 3-dehydro-D-sphinganine. |
| serine protease inhibitor complex | A heterodimeric protein complex that contains a serine protease inhibitor and a protease; formation of the complex inhibits serine protease activity. |
| serine-pyruvate aminotransferase complex | An enzyme complex that catalyzes the formation of hydroxypyruvate and alanine from serine and pyruvate. |
| serine/threonine protein kinase complex | A protein complex which is capable of protein serine/threonine kinase activity. |
| set1c/compass complex | A conserved protein complex that catalyzes methylation of histone H3. In Saccharomyces the complex contains Shg1p, Sdc1p, Swd1p, Swd2p, Swd3p, Spp1p, Bre2p, and the trithorax-related Set1p; in mammals it contains the catalytic subunit (SETD1A or SETD1B), WDR5, WDR82, RBBP5, ASH2L/ASH2, CXXC1/CFP1, HCFC1 and DPY30. |
| sex chromatin | Chromatin that is part of a sex chromosome. |
| sex chromosome | A chromosome involved in sex determination. |
| shc-egfr complex | A protein complex that contains the epidermal growth factor receptor (EGFR) and the adaptor protein Shc, and is involved in linking EGFR activation to the p21-Ras pathway. |
| sheet-forming collagen trimer | sheet-forming collagen trimer |
| short-chain collagen trimer | Any collagen trimer that does not form fibrils and that is relatively short compared to the collagen trimers that do form fibrils. |
| shu complex | A protein complex involved in error-free DNA post-replication repair (PRR). In Saccharomyces cerevisiae the complex contains Csm2p, Psy3p, Shu1p, and Shu2p. |
| side of membrane | A cellular component consisting of one leaflet of a membrane bilayer and any proteins embedded or anchored in it or attached to its surface. |
| signal peptidase complex | A protein complex that is located in the endoplasmic reticulum membrane and cleaves the signal sequence from precursor proteins following their transport out of the cytoplasmic space. |
| signal recognition particle | A complex of protein and RNA which facilitates translocation of proteins across membranes. |
| signal recognition particle receptor complex | A transmembrane heterodimeric protein located in the membrane of the rough endoplasmic reticulum. Both subunits contain GTPase domains with which signal recognition particle interacts. In the presence of GTP and SRP receptor, SRP is released from the ribosome-nascent chain complex. |
| signal recognition particle, endoplasmic reticulum targeting | A ribonucleoprotein particle of 325 kDa composed of a 7S (300 nucleotide) RNA molecule and a complex of six different polypeptides. This binds both to the N-terminal signal peptide for proteins destined for the endoplasmic reticulum as they emerge from the large ribosomal subunit and also to the ribosome. This binding arrests further translation thereby preventing the proteins from being released into the cytosol. The SRP-ribosome complex then diffuses to the endoplasmic reticulum where it is bound to the signal recognition particle receptor, which allows resumption of protein synthesis and facilitates the passage of the growing polypeptide chain through the translocon. Through a process involving GTP hydrolysis, the SRP-SRP receptor complex dissociates and SRP returns to the cytosol. Of the six polypeptides of SRP the 54 kDa subunit (SRP54) is the central player. It contains an N-terminal GTPase domain and a C-terminal domain that binds directly to the signal peptide and the SRP RNA. Examples of this component are found in Mus musculus, Saccharomyces cerevisiae and Arabidopsis thaliana. |
| sin3 complex | A multiprotein complex that functions broadly in eukaryotic organisms as a transcriptional repressor of protein-coding genes, through the gene-specific deacetylation of histones. Amongst its subunits, the Sin3 complex contains Sin3-like proteins, and a number of core proteins that are shared with the NuRD complex (including histone deacetylases and histone binding proteins). The Sin3 complex does not directly bind DNA itself, but is targeted to specific genes through protein-protein interactions with DNA-binding proteins. |
| sin3-type complex | Any of a number of evolutionarily conserved histone deacetylase complexes (HDACs) containing a core consisting of a paired amphipathic helix motif protein (e.g. Sin3p in S. cerevisiae, Pst1 in S. pombe or Sin3A in mammals) at least one class I histone deacetylase (e.g. Rpd3p in S. cerevisiae, Clr6 in S. pombe, or HDAC1 and HDAC2 in mammals), and at least one WD40 repeat protein (e.g. Ume1p in S. cerevisiae, Prw1 in S. pombe, or RbAp46 and RbAp48 in mammals). These complexes also contain a variable number of other proteins that direct histone binding, DNA binding, or add other functionality to the complex. |
| site of double-strand break | A region of a chromosome at which a DNA double-strand break has occurred. DNA damage signaling and repair proteins accumulate at the lesion to respond to the damage and repair the DNA to form a continuous DNA helix. |
| site of polarized growth | Any part of a cell where non-isotropic growth takes place. |
| ski complex | A protein complex that regulates RNA degradation by the exosome complex. In Saccharomyces the complex has a heterotetrameric stoichiometry consisting of one copy each of Ski2p and Ski3 and two copies of Ski8p. |
| slit diaphragm | A specialized cell-cell junction found between the interdigitating foot processes of the glomerular epithelium (the podocytes) in the vertebrate kidney, which is adapted for facilitating glomerular filtration. |
| slx1-slx4 complex | A heterodimeric protein complex that possesses an endonuclease activity that specifically cleaves certain types of branched DNA structures; because such structures often form during the replication ribosomal DNA (rDNA) repeats, the complex plays a role in the maintenance of rDNA. The subunits are known as Slx1 and Slx 4 in budding and fission yeasts, and are conserved in eukaryotes. |
| smad protein complex | A protein complex that consists of SMAD proteins; may be homomeric or heteromeric. |
| smad2-smad3 protein complex | A heteromeric SMAD protein complex that contains SMAD2 and SMAD3. |
| small nuclear ribonucleoprotein complex | A complex composed of RNA of the small nuclear RNA (snRNA) class and protein, found in the nucleus of a eukaryotic cell. These are typically named after the snRNA(s) they contain, e.g. U1 snRNP or U4/U6 snRNP. Many, but not all, of these complexes are involved in splicing of nuclear mRNAs. |
| small nucleolar ribonucleoprotein complex | A ribonucleoprotein complex that contains an RNA molecule of the small nucleolar RNA (snoRNA) family and associated proteins. Most are involved in a step of processing of rRNA: cleavage, 2'-O-methylation, or pseudouridylation. The majority, though not all, fall into one of two classes, box C/D type or box H/ACA type. |
| small ribosomal subunit | The smaller of the two subunits of a ribosome. |
| small-subunit processome | A large ribonucleoprotein complex that is an early preribosomal complex. In S. cerevisiae, it has a size of 80S and consists of the 35S pre-rRNA, early-associating ribosomal proteins most of which are part of the small ribosomal subunit, the U3 snoRNA and associated proteins. |
| smc loading complex | A protein complex required for the loading of a structural maintenance of chromosome (SMC) complex, such as cohesin, condensin or SMC5/SMC6, onto DNA. Appears to be eukaryotically conserved. |
| smc5-smc6 complex | A conserved complex that contains a heterodimer of SMC proteins (Smc5p and Smc6p, or homologs thereof) and several other proteins, and is involved in DNA repair and maintaining cell cycle arrest following DNA damage. In S. cerevisiae, this is an octameric complex called Mms21-Smc5-Smc6 complex, with at least five of its subunits conserved in fission yeast and humans. |
| smn complex | A protein complex that contains the survival motor neuron (SMN) protein and at least eight additional integral components, including the Gemin2-8 and Unrip proteins; the complex is found in the cytoplasm and in nuclear Gems, and is involved in spliceosomal snRNP assembly in the cytoplasm and in pre-mRNA splicing in the nucleus. |
| smn-sm protein complex | A protein complex formed by the association of several methylated Sm proteins with the SMN complex; the latter contains the survival motor neuron (SMN) protein and at least eight additional integral components, including the Gemin2-8 and unrip proteins; additional proteins, including galectin-1 and galectin-3, are also found in the SMN-SM complex. The SMN-Sm complex is involved in spliceosomal snRNP assembly in the cytoplasm. |
| smooth endoplasmic reticulum | The smooth endoplasmic reticulum (smooth ER or SER) has no ribosomes attached to it. The smooth ER is the recipient of the proteins synthesized in the rough ER. Those proteins to be exported are passed to the Golgi complex, the resident proteins are returned to the rough ER and the lysosomal proteins after phosphorylation of their mannose residues are passed to the lysosomes. Glycosylation of the glycoproteins also continues. The smooth ER is the site of synthesis of lipids, including the phospholipids. The membranes of the smooth ER also contain enzymes that catalyze a series of reactions to detoxify both lipid-soluble drugs and harmful products of metabolism. Large quantities of certain compounds such as phenobarbital cause an increase in the amount of the smooth ER. |
| smooth endoplasmic reticulum membrane | The lipid bilayer surrounding the smooth endoplasmic reticulum. |
| smooth endoplasmic reticulum part | Any constituent part of the smooth endoplasmic reticulum (also called smooth ER, or SER). |
| smooth muscle contractile fiber | The contractile fiber of smooth muscle cells. |
| snare complex | A protein complex involved in membrane fusion; a stable ternary complex consisting of a four-helix bundle, usually formed from one R-SNARE and three Q-SNAREs with an ionic layer sandwiched between hydrophobic layers. One well-characterized example is the neuronal SNARE complex formed of synaptobrevin 2, syntaxin 1a, and SNAP-25. |
| snrna-activating protein complex | A protein complex that recognizes the proximal sequence element of RNA polymerase II and III snRNA promoters. |
| sodium channel complex | An ion channel complex through which sodium ions pass. |
| sodium:potassium-exchanging atpase complex | Sodium:potassium-exchanging ATPases are tetrameric proteins, consisting of two large alpha subunits and two smaller beta subunits. The alpha subunits bear the active site and penetrate the membrane, while the beta subunits carry oligosaccharide groups and face the cell exterior. |
| sorting endosome | A multivesicular body surrounded by and connected with multiple tubular compartments with associated vesicles. |
| soss complex | A protein complex that functions downstream of the MRN complex to promote DNA repair and the G2/M checkpoint. The SOSS complex associates with single-stranded DNA at DNA lesions and is composed of SOSS-B (SOSS-B1/OBFC2B or SOSS-B2/OBFC2A), SOSS-A/INTS3 and SOSS-C/C9orf80. |
| spanning component of membrane | The component of a membrane consisting of gene products and protein complexes that have some part that spans both leaflets of the membrane. |
| spanning component of plasma membrane | The component of the plasma membrane consisting of gene products and protein complexes that have some part that spans both leaflets of the membrane. |
| specific granule | Granule with a membranous, tubular internal structure, found primarily in mature neutrophil cells. Most are released into the extracellular fluid. Specific granules contain lactoferrin, lysozyme, vitamin B12 binding protein and elastase. |
| spectrin | Membrane associated dimeric protein (240 and 220 kDa) of erythrocytes. Forms a complex with ankyrin, actin and probably other components of the membrane cytoskeleton, so that there is a mesh of proteins underlying the plasma membrane, potentially restricting the lateral mobility of integral proteins. |
| spectrin-associated cytoskeleton | The part of the cytoskeleton composed of spectrin, protein 4.1 and ankyrin. Spectrin-associated cytoskeleton is associated with the plasma membrane. |
| sperm annulus | The ring-like, filamentous structure located at the distal end of the midpiece of the sperm flagellum; the annulus is thought to form a diffusion barrier between the midpiece and the principal piece and serve as a stabilizing structure for tail rigidity. |
| sperm connecting piece | The segment of the sperm flagellum that attaches to the implantation fossa of the nucleus in the sperm head; from the remnant of the centriole at this point, the axoneme extends throughout the length of the flagellum. |
| sperm fibrous sheath | A cytoskeletal structure surrounding the axoneme and outer dense fibers of the sperm flagellum. Consists of two longitudinal columns connected by closely arrayed semicircular ribs that assemble from distal to proximal throughout spermiogenesis. The fibrous sheath probably influences the degree of flexibility, plane of flagellar motion, and the shape of the flagellar beat. |
| sperm flagellum | A microtubule-based flagellum (or cilium) that is part of a sperm, a mature male germ cell that develops from a spermatid. |
| sperm midpiece | The highly organized segment of the sperm flagellum which begins at the connecting piece and is characterized by the presence of 9 outer dense fibers (ODFs) that lie outside each of the 9 outer axonemal microtubule doublets and by a sheath of mitochondria that encloses the ODFs and the axoneme; the midpiece terminates about one-fourth of the way down the sperm flagellum at the annulus, which marks the beginning of the principal piece. |
| sperm mitochondrial sheath | The tightly packed helical sheath of ATP-producing mitochondria restricted to the midpiece of the sperm flagellum. |
| sperm part | Any constituent part of a sperm, a mature male germ cell that develops from a spermatid. |
| sperm principal piece | The segment of the sperm flagellum where the mitochondrial sheath ends, and the outer dense fibers (ODFs) associated with outer axonemal doublets 3 and 8 are replaced by the 2 longitudinal columns of the fibrous sheath (FS) which run the length of the principal piece and are stabilized by circumferential ribs. The principal piece makes up ~2/3 of the length of the sperm flagellum and is defined by the presence of the FS and of only 7 (rather than 9) ODFs which taper and then terminate near the distal end of the principal piece. |
| spherical high-density lipoprotein particle | A mature high-density lipoprotein (HDL) particle, converted from discoidal HDL particles following the esterification of cholesterol in the particle by phosphatidylcholine-sterol O-acyltransferase (lecithin cholesterol acyltransferase; LCAT). |
| spindle | The array of microtubules and associated molecules that forms between opposite poles of a eukaryotic cell during mitosis or meiosis and serves to move the duplicated chromosomes apart. |
| spindle microtubule | Any microtubule that is part of a mitotic or meiotic spindle; anchored at one spindle pole. |
| spindle midzone | The area in the center of the spindle where the spindle microtubules from opposite poles overlap. |
| spindle pole | Either of the ends of a spindle, where spindle microtubules are organized; usually contains a microtubule organizing center and accessory molecules, spindle microtubules and astral microtubules. |
| spindle pole centrosome | A centrosome from which one pole of a mitotic or meiotic spindle is organized. |
| spliceosomal complex | Any of a series of ribonucleoprotein complexes that contain RNA and small nuclear ribonucleoproteins (snRNPs), and are formed sequentially during the splicing of a messenger RNA primary transcript to excise an intron. |
| spliceosomal snrnp complex | A ribonucleoprotein complex involved in formation of the spliceosome and composed of one or more snRNA and multiple protein components. |
| spliceosomal tri-snrnp complex | A spliceosomal snRNP complex containing U4 and U6 (or U4atac and U6atac) snRNAs and U5 snRNAs and associated proteins. |
| spot adherens junction | A small cell-cell adherens junction assembled during the cellularization stage of insect embyrogenesis; spot adherens junctions later fuse to form the zonula adherens. |
| spots complex | A multiprotein complex at least composed of serine palmitoyltransferases and ORM proteins (known as ORMDL proteins in mammals and other higher vertebrates) that plays a key role in sphingolipid homeostasis. |
| srebp-scap-insig complex | A protein complex formed by the association of sterol regulatory element binding protein (SREBP), SREBP-cleavage-activating protein (SCAP), and an Insig protein (Insig-1 or Insig-2) in the ER membrane. |
| staga complex | A large multiprotein complex that possesses histone acetyltransferase and is involved in regulation of transcription. The composition is similar to that of the SAGA complex; for example, the human complex contains the transcription-transformation cofactor TRRAP, hGCN5L acetylase, novel human ADA-like and SPT-like cofactors, and a subset of TAFs. |
| stereocilia ankle link | A stereocilia coupling link that is composed of a fine filament present in developing stereocilia that couples the bases of individual stereocilia to one another. They are not present in mature stereocilia. |
| stereocilia ankle link complex | A complex of proteins that connect growing stereocilia in developing cochlear hair cells, composed of Vlgr1, usherin, vezatin, and whirlin. |
| stereocilia coupling link | A structure involved in coupling stereocilia to one another in sensory hair cells There are four morphologically distinct types: tip links, horizontal top connectors, shaft connectors and ankle links. Tip links and horizontal top connectors are the only inter-stereocilia links associated with mature cochlea, whereas ankle links appear during development of the auditory hair bundle. |
| stereocilium | An actin-based protrusion from the apical surface of auditory and vestibular hair cells. Bundles of stereocilia act as mechanosensory organelles. |
| stereocilium bundle | An actin-based, cross-linked cellular protrusion on the apical surface of auditory and vestibular hair cells. Stereocilium bundles act as mechanosensory organelles by responding to fluid motion or fluid pressure changes. |
| stereocilium bundle tip | The end of a stereocilium bundle, distal to the site of the bundle's attachment to the apical cell surface. |
| stereocilium membrane | The portion of the plasma membrane surrounding a stereocilium. |
| stn1-ten1 complex | A nuclear telomere cap complex that is formed by the association of the Stn1 and Ten1 proteins with telomeric DNA; in some species a third protein is present. |
| stress fiber | A contractile actin filament bundle that consists of short actin filaments with alternating polarity, cross-linked by alpha-actinin and possibly other actin bundling proteins, and with myosin present in a periodic distribution along the fiber. |
| striated muscle myosin thick filament | Bipolar filaments formed of polymers of a muscle-specific myosin II isoform, found in the middle of sarcomeres in myofibrils. |
| striated muscle thin filament | Filaments formed of actin and associated proteins; attached to Z discs at either end of sarcomeres in myofibrils. |
| subapical complex | The most apical region of the lateral plasma membrane of an invertebrate epithelial cell. The subapical complex lies above the zonula adherens and the septate junction, and is comparable to the position of the tight junction of vertebrate cells. |
| succinate dehydrogenase complex | A multimeric complex which consists of flavoprotein (subunit A ; InterPro:IPR003952), iron-sulfur protein (subunit B) and membrane-bound cytochrome b560 (subunit C; InterPro:IPR000701). In some Archaea, the membrane-bound subunits (C or C and D) do not necessarily contain heme. Membrane-bound subunits can bind or react with quinones. |
| succinate dehydrogenase complex (ubiquinone) | The enzyme that catalyzes the oxidation of succinate and ubiquinone to fumarate and ubiquinol; involved in aerobic respiration, repressed in anaerobic respiration. |
| succinate-coa ligase complex | A heterodimeric enzyme complex, usually composed of an alpha and beta chain. Functions in the TCA cycle, hydrolyzing succinyl-CoA into succinate and CoA, thereby forming ATP or GTP. |
| succinate-coa ligase complex (gdp-forming) | A heterodimeric enzyme complex, usually composed of an alpha and beta chain. Functions in the TCA cycle, hydrolyzing succinyl-CoA into succinate and CoA, thereby forming GTP. |
| sumo activating enzyme complex | A conserved heterodimeric complex with SUMO activating enzyme activity. |
| supraspliceosomal complex | Multicomponent complex of RNA and proteins that is composed of four active spliceosomes, termed native spliceosomes, connected to each other by the pre-mRNA. The supraspliceosome is the nuclear machine where the pre-mRNA processing takes place, like the 5'-end capping, 3'-end cleavage, splicing and editing. |
| swi/snf complex | A SWI/SNF-type complex that contains nine or more proteins, including both conserved (core) and nonconserved components; the Swi2/Snf2 ATPase is one of the core components. |
| swi/snf superfamily-type complex | A protein complex that contains an ortholog of the Saccharomyces ATPase Swi2/Snf2 as one of the core components and mediates assembly of nucleosomes, changes to the spacing or structure of nucleosomes, or some combination of those activities in a manner that requires ATP. |
| swi5-sfr1 complex | A conserved DNA recombinase mediator complex that contains two Swi5 monomers and one Sfr1 monomer in Schizosaccharomyces, or orthologs thereof (e.g. Sae3p and Mei5p in Saccharomyces). |
| swr1 complex | A multisubunit protein complex that is involved in chromatin remodeling. It is required for the incorporation of the histone variant H2AZ into chromatin. In S. cerevisiae, the complex contains Swr1p, a Swi2/Snf2-related ATPase, and 12 additional subunits. |
| symbiont-containing vacuole | Membrane-bounded vacuole within a host cell in which a symbiont organism resides. The vacuole membrane is derived from both the host and symbiont. |
| symmetric synapse | A type of synapse occurring primarily on dendrite shafts and neuronal cell bodies. Symmetric synapses involve axons containing clusters of predominantly flattened or elongated vesicles and do not contain a prominent postsynaptic density. |
| synapse | The junction between a nerve fiber of one neuron and another neuron or muscle fiber or glial cell; the site of interneuronal communication. As the nerve fiber approaches the synapse it enlarges into a specialized structure, the presynaptic nerve ending, which contains mitochondria and synaptic vesicles. At the tip of the nerve ending is the presynaptic membrane; facing it, and separated from it by a minute cleft (the synaptic cleft) is a specialized area of membrane on the receiving cell, known as the postsynaptic membrane. In response to the arrival of nerve impulses, the presynaptic nerve ending secretes molecules of neurotransmitters into the synaptic cleft. These diffuse across the cleft and transmit the signal to the postsynaptic membrane. |
| synapse part | Any constituent part of a synapse, the junction between a nerve fiber of one neuron and another neuron or muscle fiber or glial cell. |
| synaptic cleft | The narrow gap that separates the presynaptic and postsynaptic membranes, into which neurotransmitter is released. |
| synaptic membrane | A specialized area of membrane on either the presynaptic or the postsynaptic side of a synapse, the junction between a nerve fiber of one neuron and another neuron or muscle fiber or glial cell. |
| synaptic vesicle | A secretory organelle, some 50 nm in diameter, of presynaptic nerve terminals; accumulates in high concentrations of neurotransmitters and secretes these into the synaptic cleft by fusion with the 'active zone' of the presynaptic plasma membrane. |
| synaptic vesicle membrane | The lipid bilayer surrounding a synaptic vesicle. |
| synaptobrevin 2-snap-25-syntaxin-1a complex | A SNARE complex that contains synaptobrevin 2 (VAMP2), SNAP-25, and syntaxin 1a (or orthologs thereof). |
| synaptobrevin 2-snap-25-syntaxin-1a-complexin i complex | A SNARE complex that contains synaptobrevin 2 (VAMP2), SNAP-25, syntaxin 1a, and complexin I (or orthologs thereof). |
| synaptobrevin 2-snap-25-syntaxin-1a-complexin ii complex | A SNARE complex that contains synaptobrevin 2 (VAMP2), SNAP-25, syntaxin 1a, and complexin II (or orthologs thereof). |
| synaptobrevin 2-snap-25-syntaxin-3-complexin complex | A SNARE complex that contains synaptobrevin 2 (VAMP2), SNAP-25, syntaxin 3, and a complexin (or orthologs thereof). |
| synaptonemal complex | A proteinaceous scaffold found between homologous chromosomes during meiosis. |
| syntrophin complex | A protein complex that includes alpha-, beta1-, beta2-syntrophins and syntrophin-like proteins; the syntrophin complex binds to the second half of the carboxy-terminal domain of dystrophin; also associates with neuronal nitric oxide synthase. |
| t cell receptor complex | A protein complex that contains a disulfide-linked heterodimer of T cell receptor (TCR) chains, which are members of the immunoglobulin superfamily, and mediates antigen recognition, ultimately resulting in T cell activation. The TCR heterodimer is associated with the CD3 complex, which consists of the nonpolymorphic polypeptides gamma, delta, epsilon, zeta, and, in some cases, eta (an RNA splice variant of zeta) or Fc epsilon chains. |
| t-tubule | Invagination of the plasma membrane of a muscle cell that extends inward from the cell surface around each myofibril. The ends of T-tubules make contact with the sarcoplasmic reticulum membrane. |
| t-utp complex | A protein complex that forms a subcomplex of the 90S preribosome and is required for the subsequent assembly of the rest of the preribosome. In S. cerevisiae, it is composed of Utp5p, Utp4p, Nan1p, Utp8p, Utp9p, Utp10 and Utp15p. |
| tap complex | A heterodimer composed of the subunits TAP1 and TAP2 (transporter associated with antigen presentation). Functions in the transport of antigenic peptides from the cytosol to the lumen of the endoplasmic reticulum. |
| tctn-b9d complex | A protein complex that is located at the ciliary transition zone and consists of tectonic proteins, B9 domain-containing proteins and other proteins. Acts as a barrier that prevents diffusion of transmembrane proteins between the cilia and plasma membranes. In mouse, members of the complex include TCTN1, TCTN2, B9D1, MKS1, CC2D2A and other proteins. |
| telomerase holoenzyme complex | Telomerase is a ribonucleoprotein enzyme complex, with a minimal catalytic core composed of a catalytic reverse transcriptase subunit and an RNA subunit that provides the template for telomeric DNA addition. In vivo, the holoenzyme complex often contains additional subunits. |
| telomere cap complex | A complex of DNA and protein located at the end of a linear chromosome that protects and stabilizes a linear chromosome. |
| telomeric heterochromatin | Heterochromatic regions of the chromosome found at the telomeres. |
| terminal bouton | Terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. The axon terminus is considered to be the whole region of thickening and the terminal bouton is a specialized region of it. |
| terminal cisterna | The portion of sarcoplasmic reticulum devoted to calcium ion storage and calcium ion release. |
| terminal cisterna lumen | The region between the inner and outer lipid bilayers of the terminal cisterna envelope. This space is enriched in calsequestrin. |
| tertiary granule | A secretory granule that contains cathepsin and gelatinase and is readily exocytosed upon cell activation; found primarily in mature neutrophil cells. |
| tertiary granule membrane | The lipid bilayer surrounding a tertiary granule. |
| tetraspanin-enriched microdomain | A pre-organized unit composed either of adhesion molecules (mainly integrins and members of the Ig superfamily), signaling receptors and/or enzyme-enriched plasma membrane domains that compartmentalizes cellular processes. Tetraspanin-enriched microdomains might be specially suited for the regulation of avidity of adhesion receptors and the compartmentalization of enzymatic activities. |
| tfiik complex | A transcription factor complex that forms part of the holo TFIIH complex. In Saccharomyces/human, TFIIK contains Ccl1p/Cyclin H, Tfb3p/MAT1 and Kin2p/CDK7. |
| tho complex | The THO complex is a nuclear complex that is required for transcription elongation through genes containing tandemly repeated DNA sequences. The THO complex is also part of the TREX (TRanscription EXport) complex that is involved in coupling transcription to export of mRNAs to the cytoplasm. In S. cerevisiae, it is composed of four subunits: Hpr1p, Tho2p, Thp1p, and Mft1p, while the human complex is composed of 7 subunits. |
| tho complex part of transcription export complex | The THO complex when it is part of the TREX (TRanscription EXport) complex that is involved in coupling transcription to export of mRNAs to the cytoplasm. In S. cerevisiae, it is composed of four subunits: Hpr1, Tho2, Thp1, and Mft1, while the human complex is composed of 7 subunits. |
| tight junction | An occluding cell-cell junction that is composed of a branching network of sealing strands that completely encircles the apical end of each cell in an epithelial sheet; the outer leaflets of the two interacting plasma membranes are seen to be tightly apposed where sealing strands are present. Each sealing strand is composed of a long row of transmembrane adhesion proteins embedded in each of the two interacting plasma membranes. |
| tle3-aes complex | A transcriptional repressor complex that consists of a heterodimer of the proteins Tle3 (also known as Grg3b) and Aes (Grg5), which are homologs of the Drosophila groucho gene product. |
| toll-like receptor 1-toll-like receptor 2 protein complex | A heterodimeric protein complex containing Toll-like receptor 1 (TLR1) and Toll-like receptor 2 (TLR2). |
| toll-like receptor 2-toll-like receptor 6 protein complex | A heterodimeric protein complex containing Toll-like receptor 2 (TLR2) and Toll-like receptor 6 (TLR6). |
| tor complex | A protein complex that contains at least TOR (target of rapamycin) in complex with other signaling components. Mediates the phosphorylation and activation of downstream signaling components including PKB (AKT) or S6K. |
| torc1 complex | A protein complex that contains at least TOR (target of rapamycin) and Raptor (regulatory-associated protein of TOR), or orthologs of, in complex with other signaling components. Mediates the phosphorylation and activation of S6K. In Saccharomyces, the complex contains Kog1p, Lst8p, Tco89p, and either Tor1p or Tor2p. |
| torc2 complex | A protein complex that contains at least TOR (target of rapamycin) and Rictor (rapamycin-insensitive companion of TOR), or orthologs of, in complex with other signaling components. Mediates the phosphorylation and activation of PKB (also called AKT). In Saccharomyces, the complex contains Avo1p, Avo2p, Tsc11p, Lst8p, Bit61p, Slm1p, Slm2p, and Tor2p. |
| traf2-gstp1 complex | A protein complex comprising tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) and glutathione S-transferase pi 1 (GSTP1). This complex is thought to disrupt the TNF signaling cascade, thus down-regulating inflammatory responses. |
| trans-golgi network | The network of interconnected tubular and cisternal structures located within the Golgi apparatus on the side distal to the endoplasmic reticulum, from which secretory vesicles emerge. The trans-Golgi network is important in the later stages of protein secretion where it is thought to play a key role in the sorting and targeting of secreted proteins to the correct destination. |
| trans-golgi network membrane | The lipid bilayer surrounding any of the compartments that make up the trans-Golgi network. |
| trans-golgi network transport vesicle | A vesicle that mediates transport between the trans-Golgi network and other parts of the cell. |
| trans-golgi network transport vesicle membrane | The lipid bilayer surrounding a vesicle transporting substances between the trans-Golgi network and other parts of the cell. |
| transcription elongation factor complex | Any protein complex that interacts with RNA polymerase II to increase (positive transcription elongation factor) or reduce (negative transcription elongation factor) the rate of transcription elongation. |
| transcription export complex | The transcription export (TREX) complex couples transcription elongation by RNA polymerase II to mRNA export. The complex associates with the polymerase and travels with it along the length of the transcribed gene. TREX is composed of the THO transcription elongation complex as well as other proteins that couple THO to mRNA export proteins. The TREX complex is known to be found in a wide range of eukaryotes, including S. cerevisiae and metazoans. |
| transcription export complex 2 | A protein complex that couples SAGA-dependent gene expression to mRNA export at the inner side of the nuclear pore complex (NPC). The TREX-2 complex is tethered to the inner side of the NPC via the nucleoporins Nup1 and Nup60; in S. cerevisiae it contains Sac3p, Thp1p, Sus1p and Cdc31p. |
| transcription factor complex | A protein complex that is capable of associating with DNA by direct binding, or via other DNA-binding proteins or complexes, and regulating transcription. |
| transcription factor tfiia complex | A component of the transcription machinery of RNA Polymerase II. In humans, TFIIA is a heterotrimer composed of an alpha (P35), beta (P19) and gamma subunits (P12). |
| transcription factor tfiid complex | A complex composed of TATA binding protein (TBP) and TBP associated factors (TAFs); the total mass is typically about 800 kDa. Most of the TAFs are conserved across species. In TATA-containing promoters for RNA polymerase II (Pol II), TFIID is believed to recognize at least two distinct elements, the TATA element and a downstream promoter element. TFIID is also involved in recognition of TATA-less Pol II promoters. Binding of TFIID to DNA is necessary but not sufficient for transcription initiation from most RNA polymerase II promoters. |
| transcription factor tfiie complex | A transcription factor which in humans consists of a complex of two alpha and two beta chains. Recruits TFIIH to the initiation complex and helps activate both RNA polymerase II and TFIIH. |
| transcription factor tfiif complex | A general transcription initiation factor which in humans consists of a heterodimer of an alpha and a beta subunit. Helps recruit RNA polymerase II to the initiation complex and promotes translation elongation. |
| transcription factor tfiiib complex | A transcription factor complex that is involved in regulating transcription from RNA polymerase III (Pol III) promoters. TFIIIB contains the TATA-binding protein (TBP) and two Pol III-specific proteins, B'' and BRF. |
| transcription factor tfiiic complex | A heterotrimeric transcription factor complex that is involved in regulating transcription from RNA polymerase III (Pol III) promoters. TFIIIC contains three conserved subunits that associate with the proximal Pol III promoter element, and additional subunits that associate with sequence elements downstream of the promoter and are more diverged among species. It also functions as a boundary element to partition genome content into distinct domains outside Pol III promoter regions. |
| transcription factor tftc complex | A protein complex that does not contain either a TATA-binding protein (TBP) or a TBP-like factor, but is composed of several TAFIIs and other proteins, including a histone acetyltransferase. This complex is able to nucleate transcription initiation by RNA polymerase II, can mediate transcriptional activation, and has histone acetyltransferase activity. |
| transcriptional repressor complex | A protein complex that possesses activity that prevents or downregulates transcription. |
| transcriptionally active chromatin | The ordered and organized complex of DNA and protein that forms regions of the chromosome that are being actively transcribed. |
| transferase complex | A protein complex capable of catalyzing the transfer of a group, e.g. a methyl group, glycosyl group, acyl group, phosphorus-containing, or other groups, from one compound (generally regarded as the donor) to another compound (generally regarded as the acceptor). |
| transforming growth factor beta receptor homodimeric complex | A homodimeric receptor complex that consists of two TGF-beta receptor monomers. |
| translation initiation complex | A ribonucleoprotein complex that contains a ribosome, mRNA, and initiator tRNA; the functional ribosome is at the AUG, with the methionyl/formyl-methionyl-tRNA positioned at the P site. |
| translation preinitiation complex | A ribonucleoprotein complex that contains the small ribosomal subunit, a translation initiation ternary complex (i.e. an initiator tRNA, GTP, and an IF2 or eIF2 complex), and an mRNA. |
| translocon complex | A protein complex that constitutes a specific site of protein translocation across the endoplasmic reticulum, which involves the signal recognition particle receptor. The complex contains a core heterotrimer of alpha, beta and gamma subunits, and may contain additional proteins. |
| transmembrane collagen trimer | Any collagen trimer that passes through a lipid bilayer membrane. |
| transmembrane transporter complex | A transmembrane protein complex which enables the transfer of a substance from one side of a membrane to the other. |
| transport vesicle | Any of the vesicles of the constitutive secretory pathway, which carry cargo from the endoplasmic reticulum to the Golgi, between Golgi cisternae, or to destinations within or outside the cell. |
| transport vesicle membrane | The lipid bilayer surrounding a transport vesicle. |
| transporter complex | A protein complex facilitating transport of molecules (proteins, small molecules, nucleic acids) into, out of or within a cell, or between cells. |
| transverse filament | A structural unit of the synaptonemal complex that spans the regions between the lateral elements and connects them. |
| trapp complex | A large complex that acts as a tethering factor involved in transporting vesicles from the ER through the Golgi to the plasma membrane. A TRAPP (transport protein particle) complex has a core set of proteins which are joined by specific subunits depending on the cellular component where a given TRAPP complex is active. |
| tricarboxylic acid cycle enzyme complex | Any of the heteromeric enzymes that act in the TCA cycle. |
| triglyceride-rich lipoprotein particle | A plasma lipoprotein particle that has a hydrophobic core enriched in triglycerides surrounded by an amphipathic monolayer of phospholipids, cholesterol and apolipoproteins. Triglyceride-rich lipoproteinparticles transport lipids, which are non-covalently associated with the particles, in the blood. |
| trna (m1a) methyltransferase complex | A protein complex involved in the catalysis of the formation of the modified nucleotide 1-methyladenosine (m1A) in tRNA. In yeast, it is a heterotetramer of two subunits, Gcd10p and Gcd14p, while in bacteria and archaea it is a homotetramer. |
| trna methyltransferase complex | A multimeric protein complex involved in the methylation of specific nucleotides in tRNA. |
| trna-intron endonuclease complex | A protein complex that catalyzes the endonucleolytic cleavage of pre-tRNA, producing 5'-hydroxyl and 2',3'-cyclic phosphate termini, and specifically removing the intron. |
| trna-splicing ligase complex | A protein complex that catalyzes the ligation of cleaved pre-tRNAs by directly joining spliced tRNA halves to mature-sized tRNAs by incorporating the precursor-derived splice junction phosphate into the mature tRNA as a canonical 3',5'-phosphodiester. |
| troponin complex | A complex of accessory proteins (typically troponin T, troponin I and troponin C) found associated with actin in muscle thin filaments; involved in calcium regulation of muscle contraction. |
| tsc1-tsc2 complex | A protein complex consisting of at least tumerin and hamartin; its formation may regulate hamartin homomultimer formation. The complex acts as a GTPase activating protein (GAP) for the small GTPase (Rheb), and inhibits the TOR signaling pathway. |
| tubulin complex | A heterodimer of tubulins alpha and beta that constitutes the protomer for microtubule assembly. |
| type iii intermediate filament | A type of intermediate filament, typically made up of one or more of the proteins vimentin, desmin, glial fibrillary acidic protein (GFAP), and peripherin. Unlike the keratins, the type III proteins can form both homo- and heteropolymeric IF filaments. |
| u1 snrnp | A ribonucleoprotein complex that contains small nuclear RNA U1. |
| u12-type spliceosomal complex | Any spliceosomal complex that forms during the splicing of a messenger RNA primary transcript to excise an intron; the series of U12-type spliceosomal complexes is involved in the splicing of the majority of introns that contain atypical AT-AC terminal dinucleotides, as well as other non-canonical introns. The entire splice site signal, not just the terminal dinucleotides, is involved in determining which spliceosome utilizes the site. |
| u2 snrnp | A ribonucleoprotein complex that contains small nuclear RNA U2. |
| u2-type post-mrna release spliceosomal complex | A spliceosomal complex that is formed following the release of the spliced product from the post-spliceosomal complex and contains the excised intron and the U2, U5 and U6 snRNPs. |
| u2-type prespliceosome | A spliceosomal complex that is formed by association of the 5' splice site with the U1 snRNP, while the branch point sequence is recognized by the U2 snRNP. The prespliceosome includes many proteins in addition to those found in the U1 and U2 snRNPs. Commitment to a given pair of 5' and 3' splice sites occurs at the time of prespliceosome formation. |
| u2-type spliceosomal complex | Any spliceosomal complex that forms during the splicing of a messenger RNA primary transcript to excise an intron that has canonical consensus sequences near the 5' and 3' ends. |
| u4 snrnp | A ribonucleoprotein complex that contains small nuclear RNA U4. |
| u4/u6 snrnp | A ribonucleoprotein complex that contains base-paired U4 and U6 small nuclear RNAs. |
| u4/u6 x u5 tri-snrnp complex | A ribonucleoprotein complex formed by the association of the U4/U6 and U5 small nuclear ribonucleoproteins. |
| u4atac snrnp | A ribonucleoprotein complex that contains small nuclear RNA U4atac. |
| u5 snrnp | A ribonucleoprotein complex that contains small nuclear RNA U5. |
| u6 snrnp | A ribonucleoprotein complex that contains small nuclear RNA U6. |
| u7 snrnp | A ribonucleoprotein complex that contains the U7 snRNA and is required for the 3'-end processing of replication-dependent histone pre-mRNAs. |
| ubc13-mms2 complex | A heterodimeric ubiquitin conjugating enzyme complex that catalyzes assembly of K63-linked polyubiquitin chains, which act as a signal to promote error-free DNA postreplication repair; in Saccharomyces the complex comprises Ubc13p and Mms2p. |
| ubc13-uev1a complex | A heterodimeric ubiquitin conjugating enzyme complex that catalyzes assembly of K63-linked polyubiquitin chains and is involved in NF-kappaB activation. In humans at least, the complex comprises the ubiquitin-conjugating enzyme UBC13 and ubiquitin-conjugating enzyme variant 1A (UEV1A). |
| ubiquitin conjugating enzyme complex | Any complex that possesses ubiquitin conjugating enzyme activity. |
| ubiquitin ligase complex | A protein complex that includes a ubiquitin-protein ligase and other proteins that may confer substrate specificity on the complex. |
| udp-n-acetylglucosamine transferase complex | A multienzyme, heterooligomeric complex involved in dolichyl-linked oligosaccharide synthesis. In yeast the complex is composed of Alg7p, which catalyzes the first step (GlcNAc1-PP-Dol from dolichol-phosphate and UDP-GlcNAc), and Alg13p plus Alg14p, the catalytic and anchoring subunits respectively, which together catalyze the second step (GlcNAc2-PP-dolichol from GlcNAc1-PP-Dol and UDP-GlcNAc) of dolichyl-linked oligosaccharide synthesis. |
| ulk1-atg13-fip200 complex | A protein complex that is essential for mammalian autophagy, and consists of at least 3 proteins: ULK1, ATG13 and RB1CC1(FIP200). This complex is the mammalian counterpart of Atg1-Atg13-Atg17 in yeast. |
| unconventional myosin complex | A portmanteau term for myosins other than myosin II. |
| uropod | A membrane projection with related cytoskeletal components at the trailing edge of a cell in the process of migrating or being activated, found on the opposite side of the cell from the leading edge or immunological synapse, respectively. |
| uropod membrane | The portion of the plasma membrane surrounding a uropod. |
| vacuolar lumen | The volume enclosed within the vacuolar membrane. |
| vacuolar membrane | The lipid bilayer surrounding the vacuole and separating its contents from the cytoplasm of the cell. |
| vacuolar part | Any constituent part of a vacuole, a closed structure, found only in eukaryotic cells, that is completely surrounded by unit membrane and contains liquid material. |
| vacuolar proton-transporting v-type atpase complex | A proton-transporting two-sector ATPase complex found in the vacuolar membrane, where it acts as a proton pump to mediate acidification of the vacuolar lumen. |
| vacuolar proton-transporting v-type atpase, v0 domain | The V0 domain of a proton-transporting V-type ATPase found in the vacuolar membrane. |
| vacuolar proton-transporting v-type atpase, v1 domain | The V1 domain of a proton-transporting V-type ATPase found in the vacuolar membrane. |
| vacuole | A closed structure, found only in eukaryotic cells, that is completely surrounded by unit membrane and contains liquid material. Cells contain one or several vacuoles, that may have different functions from each other. Vacuoles have a diverse array of functions. They can act as a storage organelle for nutrients or waste products, as a degradative compartment, as a cost-effective way of increasing cell size, and as a homeostatic regulator controlling both turgor pressure and pH of the cytosol. |
| varicosity | Non-terminal inflated portion of the axon, containing the specialized apparatus necessary to release neurotransmitters. |
| vcb complex | A protein complex that possesses ubiquitin ligase activity; the complex is usually pentameric; for example, in mammals the subunits are pVHL, elongin B, elongin C, cullin-2 (Cul2), and Rbx1. |
| very-low-density lipoprotein particle | A triglyceride-rich lipoprotein particle that is typically composed of APOB100, APOE and APOCs and has a density of about 1.006 g/ml and a diameter of between 20-80 nm. It is found in blood and transports endogenous products (newly synthesized cholesterol and triglycerides) from the liver. |
| vesicle | Any small, fluid-filled, spherical organelle enclosed by membrane or protein. |
| vesicle coat | A membrane coat found on a coated vesicle. |
| vesicle lumen | The volume enclosed by the membrane or protein that forms a vesicle. |
| vesicle membrane | The lipid bilayer surrounding any membrane-bounded vesicle in the cell. |
| viral envelope | The lipid bilayer of a virion that surrounds the protein capsid. May also contain glycoproteins. |
| viral factory | An intracellular compartment in a host cell which increases the efficiency of viral replication and/or assembly, and shields the virus from host defenses. Viral factories can be either cytoplasmic or nuclear and often arise from extensive rearrangement of host cell cytoskeletal and/or cell membrane compartments. |
| viral membrane | The lipid bilayer of a virion, a complete fully infectious extracellular virus particle. |
| virion | The complete fully infectious extracellular virus particle. |
| virion part | Any constituent part of a virion, a complete fully infectious extracellular virus particle. |
| voltage-gated calcium channel complex | A protein complex that forms a transmembrane channel through which calcium ions may pass in response to changes in membrane potential. |
| voltage-gated potassium channel complex | A protein complex that forms a transmembrane channel through which potassium ions may cross a cell membrane in response to changes in membrane potential. |
| voltage-gated sodium channel complex | A sodium channel in a cell membrane whose opening is governed by the membrane potential. |
| wash complex | A protein complex that localizes at the surface of endosomes, where it recruits and activates the Arp2/3 complex to induce actin polymerization. In human, the WASH complex is composed of F-actin-capping protein subunits alpha and beta, WASH1, FAM21, KIAA1033, KIAA0196 and CCDC53. |
| weibel-palade body | A large, elongated, rod-shaped secretory granule characteristic of vascular endothelial cells that contain a number of structurally and functionally distinct proteins, of which the best characterized are von Willebrand factor (VWF) and P-selectin. Weibel-Palade bodies are formed from the trans-Golgi network in a process that depends on VWF, which is densely packed in a highly organized manner, and on coat proteins that remain associated with the granules. Upon cell stimulation, regulated exocytosis releases the contained proteins to the cell surface, where they act in the recruitment of platelets and leukocytes and in inflammatory and vasoactive responses. |
| x chromosome | The sex chromosome present in both sexes of species in which the male is the heterogametic sex. Two copies of the X chromosome are present in each somatic cell of females and one copy is present in males. |
| xpc complex | A nucleotide-excision repair complex that is involved in damage sensing during global genome nucleotide excision repair (GG-NER). It is part of the pre-incision (or initial recognition) complex bound to sites of DNA damage. In human, it is composed of XPC, RAD23B and CETN2. |
| xy body | A structure found in a male mammalian spermatocyte containing an unpaired X chromosome that has become densely heterochromatic, silenced and localized at the nuclear periphery. |
| y chromosome | The sex chromosome present in males of species in which the male is the heterogametic sex; generally, the sex chromosome that pairs with the X chromosome in the heterogametic sex. The Y chromosome is absent from the cells of females and present in one copy in the somatic cells of males. |
| z disc | Platelike region of a muscle sarcomere to which the plus ends of actin filaments are attached. |
| zeta dna polymerase complex | A heterodimeric DNA polymerase complex that catalyzes error-prone DNA synthesis in contexts such as translesion synthesis and double-stranded break repair. First characterized in Saccharomyces, in which the subunits are Rev3p and Rev7p; a third protein, Rev1p, is often associated with the polymerase dimer. |
| zona pellucida receptor complex | A multisubunit complex comprising the chaperonin-containing T-complex and several other components involved in mediating sperm-oocyte Interaction. |
| zonula adherens | A cell-cell adherens junction which forms a continuous belt near the apex of epithelial cells. |
| zymogen granule | A membrane-bounded, cytoplasmic secretory granule found in enzyme-secreting cells and visible by light microscopy. Contain zymogen, an inactive enzyme precursor, often of a digestive enzyme. |
| zymogen granule membrane | The lipid bilayer surrounding a zymogen granule. |
