Cdc5 interacts with the Wee1 kinase in budding yeast.

Development of a multicellular organism requires that mitosis and morphogenesis be coordinated. These processes must also be synchronized during the growth of unicellular organisms. In the yeast Saccharomyces cerevisiae, mitosis is dependent on the prior growth of a daughter cell in the form of a bud. Overexpression of wild-type Polo-like kinase Cdc5 or a catalytically inactive form resulted in the formation of multinucleate cells in budding yeast. Immunofluorescence analysis of these multinulceate cells showed that mitosis and bud formation were no longer linked. Others have shown that Swe1 is required for coupling mitosis to bud formation during a perturbed cell cycle. When the normal pathway of bud formation is perturbed, Swe1 functions to delay mitosis through negative regulation of Clb/Cdk. In cells lacking Swe1, multinucleate cells are formed in response to delays in bud formation. Affinity purification, two-hybrid analysis, and mutant characterization results suggested that Cdc5 and Swe1 interact. From these results, we conclude that multinucleate formation in response to Cdc5 overexpression is linked to titration of Swe1 function. These results also suggest that Cdc5 may be a negative regulator of Swe1.