Cell cycle: G2/M phase transition

Cell cycle progression is a tightly regulated process that depends on the expression and activation of positive and negative regulators of the cell cycle machinery. The term 'cell-cycle checkpoint' refers to mechanisms by which the cell actively halts progression through the cell cycle until it can ensure that an earlier process, such as DNA replication or mitosis, is complete. The G2 checkpoint (also known as the G2/M checkpoint) prevents cells from initiating mitosis when they experience DNA damage during G2, or when they progress into G2 with some unrepaired damage inflicted during previous phases (S or G1). The critical target of the G2 checkpoint is the mitosis-promoting activity of the cyclin B/CDK1 kinase, whose activation after various stresses is inhibited by ATM/ATR, CHK1/CHK2 and/or degradation and/or inhibition of the CDC25 family of phosphatases that normally activate CDK1 at the G2/M boundary (Kastan and Bartek, 2004).