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Background:Histones are core nuclear proteins that assemble into nucleosomes, the fundamental repeating units of eukaryotic chromatin. The N‑terminal tail of histone H4 undergoes extensive post‑translational lysine acetylation, among which Lys5, Lys8, Lys12 and Lys16 are the major physiological acetylation sites of H4, collectively referred to as H4 tetra‑acetylation (H4K5,8,12,16ac).Acetylation neutralizes the positive charge of histone tails, weakening electrostatic interactions between histones and negatively‑charged DNA, promoting chromatin decompaction and establishing permissive chromatin status for transcriptional activation. This hyperacetylated mark is enriched in euchromatic regions at active gene promoters and enhancers, serving as docking sites for bromodomain‑containing effector proteins (e.g. BRD4) to recruit transcription‑related complexes. H4 tetra‑acetylation participates in multiple key cellular events: H4K5ac/K12ac marks newly deposited histones upon chromatin assembly during DNA replication; H4K16ac contributes to higher‑order chromatin remodeling, DNA damage repair, cell senescence and dosage‑compensation pathways; global H4 hyperacetylation is also a signature epigenetic event during spermatid differentiation prior to histone‑to‑protamine exchange. Dysregulation of H4 multi‑site acetylation is closely associated with tumorigenesis, aging and developmental disorders.
