Checkpoint Kinase 1 Novocastra
Checkpoint kinase 1 (Chk1) is an evolutionary conserved protein, which in its phosphorylated form regulates cell cycle progression in response to agents that block DNA replication. Eukaryotic cells which are exposed to ionizing radiation (IR) or other genotoxic stresses activate checkpoints to delay the progression of the cell cycle. Defects in the IR-induced S phase checkpoint causes radioresistant DNA synthesis, a phenomenon reported in cancer-prone individuals suffering from ataxia-telangiectasia. Both of the cell cycle kinases, Chk1 and Chk2, act upstream of p53 in DNA damage responses. It has been reported that Chk1 mutations have been implicated in the cause of some cancers of families with Li-Fraumeni syndrome.