{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRNU4-1, the gene encoding the U4 small nuclear RNA, is essential for proper pre‐mRNA splicing. Inhibition of U4 snRNA function leads to dramatically impaired splicing activity, resulting in the accumulation of polyadenylated, unspliced transcripts that remain stably sequestered within enlarged nuclear speckles. These unprocessed pre‐mRNAs appear to be maintained in a state that permits potential completion of splicing at a later stage, emphasizing a critical quality‐control mechanism that safeguards the cell from aberrant transcript formation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn addition to its role in the major spliceosome, RNU4-1 has the capacity to engage in noncanonical interactions that can influence the specificity of intron removal. Notably, experiments employing mutant U4 snRNA designed to base pair with a mutant form of U6atac snRNA demonstrate that a U4/U6atac complex is capable of activating U12-dependent splicing. These findings indicate that, while RNU4-1 is a hallmark component of the U4/U6 di-snRNP essential for splicing most introns, its interactions can extend to modulate minor spliceosomal activity, suggesting that the specificity for splice site recognition is largely dictated by the U6 component."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nStructural studies further illuminate the functional role of RNU4-1 by revealing a highly conserved 3′ stem-loop structure capped by a UACG tetraloop. High-resolution NMR analyses have uncovered that interactions within this tetraloop—including distinctive hydrogen bonding patterns and a unique surface for potential RNA–protein or RNA–RNA contacts—may stabilize tertiary interactions essential for active spliceosome assembly. This conservation in tertiary structure underscores how RNU4-1 is optimized for its integrative role in pre-mRNA splicing."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Anne Hett, Steven West "}, {"type": "b", "children": [{"type": "t", "text": "Inhibition of U4 snRNA in human cells causes the stable retention of polyadenylated pre-mRNA in the nucleus."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "PLoS One (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1371/journal.pone.0096174"}], "href": "https://doi.org/10.1371/journal.pone.0096174"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24796696"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24796696"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Girish C Shukla, Richard A Padgett "}, {"type": "b", "children": [{"type": "t", "text": "U4 small nuclear RNA can function in both the major and minor spliceosomes."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Proc Natl Acad Sci U S A (2004)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1073/pnas.0304919101"}], "href": "https://doi.org/10.1073/pnas.0304919101"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "14691257"}], "href": "https://pubmed.ncbi.nlm.nih.gov/14691257"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Luis R Comolli, Nikolai B Ulyanov, Ana Maria Soto, et al. "}, {"type": "b", "children": [{"type": "t", "text": "NMR structure of the 3' stem-loop from human U4 snRNA."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Nucleic Acids Res (2002)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/nar/gkf560"}], "href": "https://doi.org/10.1093/nar/gkf560"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "12384583"}], "href": "https://pubmed.ncbi.nlm.nih.gov/12384583"}]}]}]}