Assembly of scaffold-mediated complexes containing Cdc42p, the exchange factor Cdc24p, and the effector Cla4p required for cell cycle-regulated phosphorylation of Cdc24p.
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.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Alleles, Binding Sites, Cell Cycle, Cell Cycle Proteins, Cytoskeleton, Fungal Proteins, Glutathione Transferase, Guanine Nucleotide Exchange Factors, Guanosine Diphosphate, Guanosine Triphosphate, Phosphoric Monoester Hydrolases, Phosphorylation, Plasmids, Precipitin Tests, Promoter Regions, Genetic, Protein Binding, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Recombinant Fusion Proteins, Saccharomyces cerevisiae Proteins, Temperature, Time Factors, cdc42 GTP-Binding Protein, p21-Activated Kinases
Adaptor Proteins, Signal Transducing, Alleles, Binding Sites, Cell Cycle, Cell Cycle Proteins, Cytoskeleton, Fungal Proteins, Glutathione Transferase, Guanine Nucleotide Exchange Factors, Guanosine Diphosphate, Guanosine Triphosphate, Phosphoric Monoester Hydrolases, Phosphorylation, Plasmids, Precipitin Tests, Promoter Regions, Genetic, Protein Binding, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Proto-Oncogene Proteins, Recombinant Fusion Proteins, Saccharomyces cerevisiae Proteins, Temperature, Time Factors, cdc42 GTP-Binding Protein, p21-Activated Kinases
J. Biol. Chem.
Date: Mar. 09, 2001
PubMed ID: 11113154
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