Checkpoint kinase 1

The DNA damage checkpoint is a signal transduction pathway that has the ability to delay entry into mitosis. When DNA is damaged, the Check point kinases (CHKs) are known to act downstream of ATM to elicit appropriate responses such as cell cycle arrest. Chk1, for instance, is activated by ATM phosphorylation of serines 123, 178, 278, and 292 of the S phase-promoting cdc25A phosphatase and accelerates IR (ionizing radiation)induced degradation of cdc25A.