The nucleotide exchange factor Cdc24p may be regulated by auto-inhibition.
Site-specific activation of the Rho-type GTPase Cdc42p by its guanine-nucleotide exchange factor (GEF) Cdc24p is critical for the establishment of cell polarity. Here we show that binding of Cdc24p to the small GTPase Rsr1p/Bud1p is required for its recruitment to the incipient bud site. Rsr1p/Bud1p binds to the CH-domain of Cdc24p, which is essential for its function in vivo. We have identified a cdc24-mutant allele, which is specifically defective for bud-site selection. Our results suggest that Cdc24p is auto-inhibited by an intramolecular interaction with its carboxy-terminal PB1-domain. Rsr1p/Bud1p appears to activate the GEF activity of Cdc24p in vivo, possibly by triggering a conformational change that dissociates the PB1-domain from its intramolecular binding site. Genetic experiments suggest that Bem1p functions as a positive regulator of Cdc24p by binding to the PB1-domain of Cdc24p, thereby preventing its re-binding to the intramolecular inhibitory site. Taken together, our results support a two-step molecular mechanism for the site-specific activation of Cdc24p, which involves Rsr1p/Bud1p and the adaptor protein Bem1p.
Swiss Institute for Experimental Cancer Research (ISREC), Epalinges/VD, Switzerland.
Yukiko
Y
Shimada
Philippe
P
Wiget
Marie-Pierre
MP
Gulli
Efrei
E
Bi
Matthias
M
Peter
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000483:Alleles; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000235:genetics*; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C073594:CDC24 protein, S cerevisiae; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D029701:Saccharomyces cerevisiae Proteins; C073129:BEM1 protein, S cerevisiae; C084013:RSR1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins