Core component of nucleosome. Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling. The nucleosome is a histone octamer containing two molecules each of H2A, H2B, H3 and H4 assembled in one H3-H4 heterotetramer and two H2A-H2B heterodimers. The octamer wraps approximately 147 bp of DNA. The chromatin-associated form, but not the free cytoplasmic form, is phosphorylated on Thr-120 by NHK-1 during mitosis, and dephosphorylated during S-phase. Also phosphorylated on Thr-120 by NHK-1 during prophase I of meiosis; which is required for acetylation of H3 'Lys-14' and H4 'Lys-5', diassembly of the synaptonemal complex, and karyosome formation. Monoubiquitination of Lys-119 by sce/dRING gives a specific tag for epigenetic transcriptional repression. Phosphorylation on Ser-2 is enhanced during mitosis. Phosphorylation on Ser-2 directly represses transcription (By similarity). Belongs to the histone H2A family.