Atypical histone H2A which can replace conventional H2A in some nucleosomes and is associated with active transcription and mRNA processing (PubMed:22795134). 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 (PubMed:15257289, PubMed:16287874, PubMed:16957777, PubMed:17591702, PubMed:17726088, PubMed:18329190, PubMed:22795134). Nucleosomes containing this histone are less rigid and organize less DNA than canonical nucleosomes in vivo (PubMed:15257289, PubMed:16957777, PubMed:17591702, PubMed:24336483). They are enriched in actively transcribed genes and associate with the elongating form of RNA polymerase (PubMed:17591702, PubMed:24753410). They associate with spliceosome components and are required for mRNA splicing (PubMed:22795134). {ECO:0000269|PubMed:15257289, ECO:0000269|PubMed:16287874, ECO:0000269|PubMed:16957777, ECO:0000269|PubMed:17591702, ECO:0000269|PubMed:17726088, ECO:0000269|PubMed:18329190, ECO:0000269|PubMed:22795134, ECO:0000269|PubMed:24336483, ECO:0000269|PubMed:24753410}. This is the function of ENSG00000274183 (H2AB1, H2A.B variant histone 1).