Variant histone H2A which replaces conventional H2A in a subset of nucleosomes where it represses transcription (PubMed:12718888, PubMed:15621527, PubMed:16428466). Nucleosomes wrap and compact DNA into chromatin, limiting DNA accessibility to the cellular machineries which require DNA as a template (PubMed:15897469). Histones thereby play a central role in transcription regulation, DNA repair, DNA replication and chromosomal stability (PubMed:15897469). DNA accessibility is regulated via a complex set of post-translational modifications of histones, also called histone code, and nucleosome remodeling. Involved in stable X chromosome inactivation (PubMed:15897469). Inhibits the binding of transcription factors, including NF-kappa-B, and interferes with the activity of remodeling SWI/SNF complexes (PubMed:12718888, PubMed:16428466). Inhibits histone acetylation by EP300 and recruits class I HDACs, which induces a hypoacetylated state of chromatin (PubMed:16107708, PubMed:16428466). ; [Isoform 1]: Isoform that specifically binds poly-ADP-ribose and O-acetyl-ADP-ribose and plays a key role in NAD(+) metabolism (PubMed:15902274). Able to bind to the ends of poly-ADP-ribose chains created by PARP1 and cap them (By similarity). This prevents PARP1 from further addition of ADP-ribose and thus limits the consumption of nuclear NAD(+), allowing the cell to maintain proper NAD(+) levels in both the nucleus and the mitochondria to promote proper mitochondrial respiration (By similarity). Increases the expression of genes involved in redox metabolism, including SOD3 (PubMed:23022728). ; [Isoform 2]: In contrast to isoform 1, does not bind poly-ADP-ribose (PubMed:15902274). Represses SOD3 gene expression (PubMed:23022728).
