Abstract
Inactivation of cyclin-dependent kinase (Cdk) and reversal of Cdk phosphorylation are universally required for mitotic exit. In budding yeast (Saccharomyces cerevisiae), Cdc14 is essential for both and thought to be the major Cdk-counteracting phosphatase. However, Cdc14 is not required for mitotic exit in many eukaryotes, despite highly conserved biochemical properties. The question of how similar enzymes could have such disparate influences on mitotic exit prompted us to re-examine the contribution of budding yeast Cdc14. By using an auxin-inducible degron, we show that severe Cdc14 depletion has no effect on the kinetics of mitotic exit and bulk Cdk substrate dephosphorylation, but causes a cell separation defect and is ultimately lethal. Phosphoproteomic analysis revealed that Cdc14 is highly selective for distinct Cdk sites in vivo and does not catalyze widespread Cdk substrate dephosphorylation. We conclude that additional phosphatases likely contribute substantially to Cdk substrate dephosphorylation and coordination of mitotic exit in budding yeast, similar to in other eukaryotes, and the critical mitotic exit functions of Cdc14 require trace amounts of enzyme. We propose that Cdc14 plays very specific, and often different, roles in counteracting Cdk phosphorylation in all species.