Phosphorylation of Bem2p and Bem3p may contribute to local activation of Cdc42p at bud emergence

EMBO J. 2007 Oct 31;26(21):4501-13. doi: 10.1038/sj.emboj.7601873. Epub 2007 Oct 4.


Site-specific activation of the Rho-type GTPase Cdc42p is critical for the establishment of cell polarity. Here we investigated the role and regulation of the GTPase-activating enzymes (GAPs) Bem2p and Bem3p for Cdc42p activation and actin polarization at bud emergence in Saccharomyces cerevisiae. Bem2p and Bem3p are localized throughout the cytoplasm and the cell cortex in unbudded G1 cells, but accumulate at sites of polarization after bud emergence. Inactivation of Bem2p results in hyperactivation of Cdc42p and polarization toward multiple sites. Bem2p and Bem3p are hyperphosphorylated at bud emergence most likely by the Cdc28p-Cln2p kinase. This phosphorylation appears to inhibit their GAP activity in vivo, as non-phosphorylatable Bem3p mutants are hyperactive and interfere with Cdc42p activation. Taken together, our results indicate that Bem2p and Bem3p may function as global inhibitors of Cdc42p activation during G1, and their inactivation by the Cdc28p/Cln kinase contributes to site-specific activation of Cdc42p at bud emergence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle
  • Cell Cycle Proteins / metabolism
  • Cytoplasm / metabolism
  • G1 Phase
  • GTPase-Activating Proteins / metabolism*
  • Gene Expression Regulation, Fungal*
  • Phosphorylation
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Two-Hybrid System Techniques
  • cdc42 GTP-Binding Protein / metabolism*


  • BEM2 protein, S cerevisiae
  • BEM3 protein, S cerevisiae
  • Cell Cycle Proteins
  • GTPase-Activating Proteins
  • Saccharomyces cerevisiae Proteins
  • cdc42 GTP-Binding Protein