H2A is a core component of nucleosome. A nucleosome is the basic repeating unit of chromatin in which 146 base pairs of DNA wrap twice around an octamer of histones. The octamer is composed of two of each histone H2A, H2B, H3, and H4. DNA accessibility is regulated via a complex set of post-translational modifications of these histones, also called histone code, and nucleosome remodeling. Histones H2A and H2B form a dimer. Histones H3 and H4 form a tetramer. The combination of two H2A/H2B dimers and one H3/H4 tetramer create the nucleosome core. Histone H4 undergoes many modifications which include acetylation, phosphorylation and methylation that are important for regulation of gene transcription. Nucleosomes wrap and compact DNA into chro