Anti-H2A clustered histone 21 antibodies are used for the immunodetection of the protein encoded by the H2AC21 gene. In humans, the canonical protein has a reported length of 130 amino acid residues and a mass of 14 kDa. Its subcellular localization is in the nucleus and chromosomes. A member of the Histone H2A protein family, it is an important component of nucleosome. Post-translational modifications have been described, including ubiquitination, acetylation and phosphorylation. Other names for this target antigen include histone 2, H2ab, histone cluster 2 H2A family member b, histone cluster 2, H2ab, and histone H2A type 2-B. Gene orthologs have been identified in the mouse, rat, bovine and chimpanzee species.