Recombinant human MAPKAP Kinase 2, amino acids 46-400, A399G, containing an N-terminal GST tag. MAPKAP Kinase 2 has been implicted as a cell cycle checkpoint kinase, joining the ranks of Chk1 and Chk2 as critical regulators of the DNA damage response in mammalian cells in recent studies (Manke, et al, 2005, and Abraham, 2005). This research indicates that MAPKAP Kinase 2, a serine/threonine kinase activated by p38, phosphorylates CDC25 B/C, generating a binding site for 14-3-3 proteins. The checkpoint kinases Chk1 and Chk2 are targets for drug discovery efforts designed to overcome cell cycle arrest due to DNA damage induced by chemotherapeutic agents. Overriding the checkpoint kinases in cancer cells exposed to DNA damaging agents leads to catastrophic failure of cell division and apoptosis. The new role of MAPKAP Kinase 2 in complementing the function of Chk1 and Chk2 suggests a new target for drug discovery efforts.