Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 276, Issue 10, Pages 7176-7186Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M010546200
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- NIGMS NIH HHS [GM53050] Funding Source: Medline
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In budding yeast cells, the cytoskeletal polarization and depolarization events that shape the bud are triggered at specific times during the cell cycle by the cyclin-dependent kinase Cdc28p, Polarity establishment also requires the small GTPase Cdc42p and its exchange factor, Cdc24p, but the mechanism whereby Cdc28p induces Cdc42p-dependent polarization is unknown. Here we show that Cdc24p becomes phosphorylated in a cell cycle-dependent manner, triggered by Cdc28p, However, the role of Cdc28p is indirect, and the phosphorylation appears to be catalyzed by the pal-activated kinase family member Cla4p and also depends on Cdc42p and the scaffold protein Bem1p, Expression of GTP-Cdc42p, the product of Cdc24p-mediated GDP/GTP exchange; stimulated Cdc24p phosphorylation independent of cell cycle cues, raising the possibility that the phosphorylation is part of a feedback regulatory pathway. Bem1p binds directly to Cdc24p, to Cla4p, and to GTP-bound Cdc42p and can mediate complex formation between these proteins in vitro. We suggest that Bem1p acts to concentrate polarity establishment proteins at a discrete site, facilitating polarization and promoting Cdc24p phosphorylation at specific times during the cell cycle.
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