Atypical histone H2A which can replace conventional H2A in some nucleosomes and is associated with active transcription and mRNA processing. 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. Nucleosomes containing this histone are less rigid and organize less DNA than canonical nucleosomes in vivo. They are enriched in actively transcribed genes and associate with the elongating form of RNA polymerase. They associate with spliceosome components and are required for mRNA splicing. May participate in spermatogenesis. 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. May be incorporated into a proportion of nucleosomes, replacing one or more H2A molecules. Associated with the active X chromosome and with autosomes, while it is absent from the inactive X chromosome and excluded from Barr bodies. Present in mature sperm. The docking domain is responsible for the weaker heterodimerization with H2B. In contrast to other H2A histones, it does not contain the conserved residues that are the target of post-translational modifications. Belongs to the histone H2A family. Histone H2A entry