Getting In and Out of Mitosis

There are two major problems for the cell to solve in mitosis: how to ensure that each daughter cell receives an equal and identical complement of the genome, and how to prevent cell separation before chromosome segregation. Both these problems are solved by controlling when two specific proteins are destroyed: securin, an inhibitor of chromosome segregation, and cyclin B, which inhibits cell separation (cytokinesis). It has recently become clear that a number of other proteins are degraded at specific points in mitosis. This review will focus on how specific proteins are selected for proteolysis at defined points inmitosis and how this selection contributes to the proper coordination of chromosome segregation and cytokinesis.