Protein Phosphatases Take the Mitotic Stage

Following the identification of cyclin-dependent kinases in the 1980s, kinases were hailed as the directors of mitosis. Although the action of kinases must necessarily be reversible, only recently has the involvement of specific phosphatases in mitosis become appreciated. Studies are now revealing how the timely execution of mitotic events depends on the delicate interplay between kinases and phosphatases. To date, the best-characterized mitotic phosphatases are Cdc25, that is required for entry into mitosis and Cdc14, that controls exit from mitosis in budding yeast. Recent work has now exposed the conserved serine-threonine phosphatases PP1 and PP2A as key regulators of various mitotic processes.