Checkpoint Kinase (Chk)

DNA damage checkpoint and the spindle checkpoint are two cell cycle surveillance systems, which guard against genomic instability. The DNA damage checkpoint kinases CHK1 and CHK2 are central to the induction of cell cycle arrest, DNA repair, and apoptosis as elements in the DNA-damage checkpoint. The components of the spindle checkpoint include Mad1, Mad2, Mad3(BubR1), Bub3 and the kinases Bub1, Mph1(Mps1) and Aurora B.

Cells that suffer DNA damage activate the checkpoint kinases CHK1 and CHK2, which signal to initiate repair processes, limit cell-cycle progression and prevent cell replication, until the damaged DNA is repaired.

The spindle checkpoint causes metaphase arrest when kinetochore-microtubules are unattached during mitosis. The SAC consists of ‘sensor’ proteins, such as Mad1, Bub1 and Mps1; a ‘signal transducer’, consisting of the mitotic checkpoint complex, composed of Mad2, Bub3, BubR1 and Cdc20; and an ‘effector’ known as the anaphase promoting complex/cyclosome (APC/C).