Fig. 1.

Schematic of histone modifications and modifiers. (A) DNA is compacted in the nucleus. The fundamental repeating unit of chromatin is the nucleosome, which consists of 147 base pairs of DNA wrapped around an octamer of the following core histone proteins: H2A, H2B, H3, and H4. Histone proteins consist of less structured amino-terminal tails (tail domain) that protrude from the nucleosome and globular carboxy-terminal domains make up the nucleosome scaffold (fold domain). The histone tail domain could be a target of a variety of post-translational modifications, including acetylation (Ac), methylation (Me) and ubiquitination of lysine (K) residues, phosphorylation (P) of serine (S) and threonine (T) residues, and methylation of arginine (R) residues. (B) Lysine residues in the histone H3 tail are the targets of methyltransferases and demethylases. Histone methylase, MLL, myeloid/lymphoid or mixed-lineage leukemia; SMYD3, SET and MYND domain containing 3; RIZ1, retinoblastoma protein-interacting zinc-finger protein 1; EZH2, enhancer of zeste homologue 2; NSD1, Nuclear receptor binding SET domain protein 1. Histone demethylases, LSD1, lysine-specific histone demethylase 1; SMCX, Smcx homolog, X chromosome; SMCY, Smcy homolog, Y chromosome.⁴²