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.