Accurate genome segregation depends on cohesion mechanisms that link duplicated sister chromatids, thereby allowing their tension-dependent biorientation in metaphase. In Saccharomyces cerevisiae, cohesion is established during DNA replication when Eco1 acetylates the cohesin subunit Smc3. Cohesion establishment is restricted to S phase of the cell cycle, but the molecular basis of this regulation is unknown. Here, we show that Eco1 is negatively regulated by the protein kinase Cdk1. Phosphorylation of Eco1 after S phase targets it to SCF(Cdc4) for ubiquitination and subsequent degradation. A nonphosphorylatable mutant of Eco1 establishes cohesion after DNA replication, suggesting that Cdk1-dependent phosphorylation of Eco1 is a key factor limiting establishment to S phase. We also show that deregulation of Eco1 results in chromosome separation defects in anaphase. We conclude that this regulatory mechanism helps optimize the level of sister chromatid cohesion, ensuring a robust and efficient anaphase.
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