Checking out the G2/M transition

Tight regulation of cell cycle progression is essential for the maintenance of genomic integrity. The orderly progression from one cell cycle phase to the other is mediated by timed activation of distinct cyclin/cdk complexes. For example, onset of mitosis is regulated by the activation of cyclin B/cdc2 and this event is controlled by several cell cycle checkpoints. Such checkpoints ensure that chromosome segregation does not occur in the case of unreplicated or damaged DNA, or misaligned chromosomes. Recently, new insights into the targets of the DNA damage checkpoint help to unravel more of the complex mechanisms of cell cycle checkpoints. This review focuses on the factors controlling the transition from G(2) phase to mitosis. Also, the pathways contributing to the DNA damage checkpoints in these phases of the cell cycle will be discussed. (C) 2001 Elsevier Science B.V. All rights reserved.