Anti-H2AX antibodies are directed against the protein encoded by the gene H2A.X variant histone alias H2A.X, H2A/X, H2AFX, histone H2AX, H2A histone family member X, H2AX histone, histone H2A.x. The H2AX gene in humans encodes a 143-amino acid protein with a predicted mass of 15.1 kDa and belonging to the Histone H2A family. The protein, which has a nuclear localization, is involved with the cellular response to DNA damage stimulus and cellular response to gamma radiation. Orthologs are found in mice, rats, bovines, canines, chicken, chimpanzees, guinea pigs, horses, porcine, rabbits, rhesus monkeys, and sheep.