Variant histone H2A which replaces conventional H2A in a subset of nucleosomes. 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. Acts as a Polycomb group (PcG) protein required to maintain the transcriptionally repressive state of homeotic genes of the animal throughout development. Required for histone H3 'Lys-9' methylation and histone H4 'Lys-12' acetylation, two modifications that are essential for heterochromatin formation. Also involved in DNA double strand break (DSB) repair. Essential for early development. 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. H2A or its variant His2Av forms a heterodimer with H2B. Widely distributed in the genome, irrespective of the transcriptional status or coding capacity of the sequence. Expressed both maternally and zygotically. Expressed in embryos and adults (females only). The [ST]-Q motif constitutes a recognition sequence for kinases from the PI3/PI4-kinase family. Phosphorylated. Phosphorylation of Ser-138 occurs in response to DNA double strand breaks (DSBs) generated by exogenous genotoxic agents. Phosphorylation is dependent on the DNA damage checkpoint kinases ATR and ATM, spreads on either side of a detected DSB site and may mark the surrounding chromatin for recruitment of proteins required for DNA damage signaling and repair. Acetylated on Lys-5 by Tip60. Acetylation is enhanced by Ser-138 phosphorylation and promotes the exchange of the phosphorylated form with the unmodified form of H2AV. Monoubiquitination of Lys-121 by sce/dRING gives a specific tag for epigenetic transcriptional repression. Belongs to the histone H2A family.