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Original Article |
Correspondence to: Kyung S. Lee, Laboratory of Metabolism, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bldg. 37, Rm. 3D25, Bethesda, MD 20892. Tel:(301) 496-9635 Fax:(301) 496-8419 E-mail:kyunglee{at}pop.nci.nih.gov.
Coordination of mitotic exit with timely initiation of cytokinesis is critical to ensure completion of mitotic events before cell division. The Saccharomyces cerevisiae polo kinase Cdc5 functions in a pathway leading to the degradation of mitotic cyclin Clb2, thereby permitting mitotic exit. Here we provide evidence that Cdc5 also plays a role in regulating cytokinesis and that an intact polo-box, a conserved motif in the noncatalytic COOH-terminal domain of Cdc5, is required for this event. Depletion of Cdc5 function leads to an arrest in cytokinesis. Overexpression of the COOH-terminal domain of Cdc5 (cdc5
N), but not the corresponding polo-box mutant, resulted in connected cells. These cells shared cytoplasms with incomplete septa, and possessed aberrant septin ring structures. Provision of additional copies of endogenous CDC5 remedied this phenotype, suggesting a dominant-negative inhibition of cytokinesis. The polo-box–dependent interactions between Cdc5 and septins (Cdc11 and Cdc12) and genetic interactions between the dominant-negative cdc5N and Cyk2/Hof1 or Myo1 suggest that direct interactions between cdc5N and septins resulted in inhibition of Cyk2/Hof1- and Myo1-mediated cytokinetic pathways. Thus, we propose that Cdc5 may coordinate mitotic exit with cytokinesis by participating in both anaphase promoting complex activation and a polo-box–dependent cytokinetic pathway.
Key Words: Cdc5, polo-box, mitosis, cytokinesis, septin
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