Histone modification

Histone modifications are post‑translational chemical changes to histone proteins (for example, acetylation, methylation, phosphorylation and ubiquitination) that alter chromatin structure and influence gene expression. Modifications to histone tails affect how tightly DNA is packaged and how accessible it is to transcription factors.

Common effects:

• Acetylation of lysine residues (by histone acetyltransferases, HATs) is generally associated with open chromatin and active transcription; deacetylation (by histone deacetylases, HDACs) is linked to repression.
• Lysine methylation can activate or repress transcription depending on the residue (for example, H3K4me3 is associated with active promoters; H3K27me3 with repressed regions).

Clinical relevance: Histone‑modifying enzymes are drug targets in cancer and are studied in neurology and psychiatry research.

See also: Epigenetics, DNA methylation.