Anti-ATR antibodies are used in the immunodetection of the protein ATR serine/threonine kinase. In humans, the canonical protein has a reported length of 2644 amino acid residues and a mass of 301.4 kDa. Its subcellular localization is in the nucleus. Alternative splicing is reported to yield 3 different isoforms for this protein. It is found to be widely expressed, with highest expression in testis. A member of a the PI3/PI4-kinase protein family, ATR is a serine/threonine protein kinase which activates checkpoint signaling upon genotoxic stresses such as ionizing radiation (IR), ultraviolet light (UV), or DNA replication stalling, thereby acting as a DNA damage sensor. Post-translational modifications have been described, including phosphorylation. Synonyms for this target antigen include FRP1, MEC1, SCKL, SCKL1, serine/threonine-protein kinase ATR, and FCTCS.