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After anaphase, the high mitotic cyclin-dependent kinase (Cdk) activity is downregulated to promote exit from mitosis. To this end, in the budding yeast S. cerevisiae, the Cdk counteracting phosphatase Cdc14 is activated. In metaphase, Cdc14 is kept inactive in the nucleolus by its inhibitor Net1. During anaphase, Cdk- and Polo-dependent phosphorylation of Net1 is thought to release active Cdc14. How Net1 is phosphorylated specifically in anaphase, when mitotic kinase activity starts to decline, has remained unexplained. Here, we show that PP2A(Cdc55) phosphatase keeps Net1 underphosphorylated in metaphase. The sister chromatid-separating protease separase, activated at anaphase onset, interacts with and downregulates PP2A(Cdc55), thereby facilitating Cdk-dependent Net1 phosphorylation. PP2A(Cdc55) downregulation also promotes phosphorylation of Bfa1, contributing to activation of the "mitotic exit network" that sustains Cdc14 as Cdk activity declines. These findings allow us to present a new quantitative model for mitotic exit in budding yeast.

Type

Journal article

Journal

Cell

Publication Date

2006

Volume

125

Pages

719 - 732

Keywords

Cell Cycle Proteins/genetics/*metabolism Cell Nucleolus/metabolism Cyclin B/genetics/metabolism Down-Regulation Endopeptidases/genetics/*metabolism Enzyme Activation Mitosis/*physiology Models, Biological Nuclear Proteins/genetics/metabolism Phosphoprotein Phosphatases/genetics/*metabolism Phosphorylation Protein Tyrosine Phosphatases/genetics/metabolism Saccharomyces cerevisiae/cytology/*physiology Saccharomyces cerevisiae Proteins/genetics/metabolism