Abstract
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 p21-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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adaptor Proteins, Signal Transducing
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Alleles
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Binding Sites
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Cell Cycle / physiology*
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Cell Cycle Proteins / chemistry*
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Cytoskeleton / chemistry*
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Cytoskeleton / metabolism
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Fungal Proteins / metabolism
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Glutathione Transferase / metabolism
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Guanine Nucleotide Exchange Factors*
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Guanosine Diphosphate / metabolism
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Guanosine Triphosphate / metabolism
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Phosphoric Monoester Hydrolases / metabolism
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Phosphorylation
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Plasmids / metabolism
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Precipitin Tests
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Promoter Regions, Genetic
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Protein Binding
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Protein Serine-Threonine Kinases / chemistry*
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Protein Serine-Threonine Kinases / metabolism
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Protein Structure, Tertiary
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Proto-Oncogene Proteins / chemistry*
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Recombinant Fusion Proteins / metabolism
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Saccharomyces cerevisiae Proteins*
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Temperature
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Time Factors
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cdc42 GTP-Binding Protein / chemistry*
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p21-Activated Kinases
Substances
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Adaptor Proteins, Signal Transducing
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CDC24 protein, S cerevisiae
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Cell Cycle Proteins
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Fungal Proteins
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Guanine Nucleotide Exchange Factors
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Proto-Oncogene Proteins
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Recombinant Fusion Proteins
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Saccharomyces cerevisiae Proteins
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Guanosine Diphosphate
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BEM1 protein, S cerevisiae
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Guanosine Triphosphate
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Glutathione Transferase
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CLA4 protein, S cerevisiae
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Protein Serine-Threonine Kinases
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p21-Activated Kinases
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Phosphoric Monoester Hydrolases
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cdc42 GTP-Binding Protein