{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Histone H4C2, as a core component of the nucleosome, plays a central role in orchestrating chromatin structure and function through a variety of post‐translational modifications that integrate cellular signals to regulate transcription, DNA repair, cell cycle progression, and centromere identity. For example, acetylation at lysine 16 on histone H4 (H4K16Ac) inhibits compaction of nucleosomal arrays and modulates interactions with remodeling enzymes – a regulatory mechanism that influences higher order chromatin organization and facilitates proper DNA repair and mitotic progression (see."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In addition, specific methylation marks on histone H4—such as dimethylation at lysine 20 (H4K20me2)—serve as binding platforms for key DNA damage response factors like 53BP1, thereby targeting repair proteins to sites of double-strand breaks."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": " Acetylated H4 is also selectively recognized by bromodomain-containing proteins; for instance, BRD4’s tandem bromodomains bind di‐ or tetra–acetylated H4 tails, which underpins its role in mediating transcription and chromatin remodeling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n The dynamic regulation of H4 modifications is further exemplified during mitosis, where deacetylation of H4K16 by sirtuins, such as SirT2, facilitates chromatin condensation required for accurate chromosome segregation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": " In the context of centromere assembly, H4 associates with CENP-A to form uniquely compact, sub‐nucleosomal tetramers that are essential for centromere identity and stability."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Moreover, additional layers of regulation are provided by demethylases such as JMJD6—which targets arginine residues on H4—and PHF8, which specifically demethylates H4K20me1, thereby influencing cell cycle transitions and DNA repair pathways."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "10"}]}, {"type": "t", "text": " Acetylation of H4 at DNA damage sites, mediated by histone acetyltransferase (HAT) complexes (including Trrap–Tip60), promotes chromatin relaxation for the timely recruitment of repair factors."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n In summary, H4C2 functions as a multifaceted scaffold whose post‐translational modifications—acetylation, methylation, and demethylation—integrate diverse intracellular cues. 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