Fig. 2. A schematic diagram of histone modification.

(A) Histone acetylation: Acetylation and deacetylation are catalyzed by histone acetyltransferase and histone deacetylase, respectively. Acetyl-CoA is a source and co-factor of acetylation. Histone acetylation occurs at lysine residues and it increases gene expression in general. (B) Histone methylation: Methylation is catalyzed by histone methyltransferase. Histone demethylase reverses methylation. Methylation activates or represses gene expression depending on which residue is methylated. K4 methylation activates gene expression. K27 methylation represses gene expression. (C) Histone phosphorylation; Phosphorylation is catalyzed by kinases. Phosphorylation takes place on the C-terminal tail and N-terminal structure. ATP is a source of phosphorylation. Histone phosphorylation is not only associated with gene expression control, but also chromatin condensation following cell cycle and DNA damage. Phosphatases remove phosphate groups.

Ac, acetylation; Me, methylation; P, phosphorylation.