A stage in the cell cycle at which progress can be halted if the appropriate conditions are not met. Major checkpoints, at which cdc proteins act, are at the G1/S and G2/M boundaries. Checkpoint kinases (CHK1, CHK2, EC 188.8.131.52) are serine/threonine kinases that act downstream of ATM in response to detection of DNA damage. Chk 1 (476 aa) is essential for normal cell division and Chk 2 is mutated in many tumours. Chk2 (543 aa), along with ATM regulates the transcription factor p53 by preventing its ubiquitination by the RING E3 ligase Mdm2 and is defective in Li–Fraumeni syndrome-2.
Subjects: Science and Mathematics — Medicine and Health.