May act as an acrosome-nuclear docking protein in sperm. Subacrosomal region. Does not localize in nucleus (By similarity). Present in testis (at protein level) (PubMed:11784042, PubMed:17261847). Not detected in other tissues tested (PubMed:17261847). Highly expressed during late spermiogenesis, in condensing spermatids (at protein level). Expression persists in mature spermatozoa (at protein level). Expression is first detected from the round spermatid stage and increases thereafter. Belongs to the histone H2B family.