Atypical histone H2A which can replace conventional H2A in some nucleosomes and may play a role during spermatogenesis. 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. 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. Interacts with H2BC1/TH2B; preferentially dimerizes with H2BC1/TH2B to form nucleosomes (PubMed:17261847). Specifically localizes to the pericentric regions in condensing spermatids (PubMed:17261847). Testis-specific. Strongly enriched in step 12-16 spermatids and accumulate during late spermiogenesis, in condensing spermatids (PubMed:17261847). Remains present in mature spermatozoa isolated from epididymis (PubMed:17261847). Rapidly disappears from the paternal pericentric heterochromatin regions after sperm-egg fusion (PubMed:18703863). 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.