Merck, 05-636-I, Anti-phospho-Histone H2A.X (Ser139) Antibody, clone JBW301

The histone H2A.X protein is a variant member of the H2A family of histones that is distinguished from other H2A histones by a unique carboxy-terminal sequence. This unique sequence is highly conserved throughout eukaryotic evolution and is rapidly phosphorylated by ATM or ATR at the fourth residue from the carboxy-terminus (Serine 139 in mammalian H2A.X) in response to DNA double-strand breaks (DSBs). Phosphorylation of H2A.X is important in the formation of a stable repair complex at the site of DNA damage.H2A.X phosphorylation is a very rapid response to DNA damage, occurring within as little as one minute after exposure to ionizing radiation. Phosphorylation of H2A.X occurs irrespective of the cause of the DNA DSBs and phospho-H2A.X has been observed in response to environmental stresses that result in DSBs as well as programmed cellular events, including DNA rearrangement and apoptosis.