title: Activation of the Cdc42p GTPase by cyclin-dependent protein kinases in budding yeast.
abstract: Cyclin-dependent kinases (CDKs) trigger essential cell cycle processes including critical events in G1 phase that culminate in bud emergence, spindle pole body duplication, and DNA replication. Localized activation of the Rho-type GTPase Cdc42p is crucial for establishment of cell polarity during G1, but CDK targets that link the Cdc42p module with cell growth and cell cycle commitment have remained largely elusive. Here, we identify the GTPase-activating protein (GAP) Rga2p as an important substrate related to the cell polarity function of G1 CDKs. Overexpression of RGA2 in the absence of functional Pho85p or Cdc28p CDK complexes is toxic, due to an inability to polarize growth. Mutation of CDK consensus sites in Rga2p that are phosphorylated both in vivo and in vitro by Pho85p and Cdc28p CDKs results in a loss of G1 phase-specific phosphorylation. A failure to phosphorylate Rga2p leads to defects in localization and impaired polarized growth, in a manner dependent on Rga2p GAP function. Taken together, our data suggest that CDK-dependent phosphorylation restrains Rga2p activity to ensure appropriate activation of Cdc42p during cell polarity establishment. Inhibition of GAPs by CDK phosphorylation may be a general mechanism to promote proper G1-phase progression.
authors.affiliation: Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Richelle
authors.initials: R
authors.lastname: Sopko
authors.forename: Dongqing
authors.initials: D
authors.lastname: Huang
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Smith
authors.forename: Daniel
authors.initials: D
authors.lastname: Figeys
authors.forename: Brenda J
authors.initials: BJ
authors.lastname: Andrews
mesh_terms: D002453:Cell Cycle; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D016193:G1 Phase; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D008954:Models, Biological; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D018844:Cyclin-Dependent Kinases; C058605:PHO85 protein, S cerevisiae; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020764:cdc42 GTP-Binding Protein