During the cell cycle, the cyclin-dependent kinases (CDKs) at the center of the cell cycle clock trigger a diverse set of events, including remodeling of the cell’s cytoskeleton. A number of internal surveillance pathways called checkpoint controls assess how key events are progressing and, if there is a hitch in some important process, they signal the clock to wait until the defect is corrected. In the past few years we have learned a lot about how the central clock works. However, several central questions remain concerning how the CDKs actually trigger many of the events, and how the checkpoint controls “know” whether things are proceeding according to plan.
