title: Genetic evidence for the roles of the bud-site-selection genes BUD5 and BUD2 in control of the Rsr1p (Bud1p) GTPase in yeast.
abstract: Yeast cells normally display either an axial (for MATa or MAT alpha cells) or bipolar (for MATa/alpha cells) pattern of bud-site selection. The RSR1 gene, which was previously identified as a multicopy suppressor of Ts- mutations in the bud-emergence gene CDC24, encodes a GTPase of the Ras family that is required for both budding patterns. Mutations in Rsr1p that presumably block its ability to bind or hydrolyze GTP cause a randomized budding phenotype, suggesting that regulators of Rsr1p will prove to be required for proper bud positioning. The BUD5 gene product is required for proper bud-site selection and contains similarity to GDP-dissociation stimulators (GDS) for Ras-type proteins, suggesting that Bud5p may be a GDS for Rsr1p. Here I report that BUD5 is required for wild-type RSR1, but not for mutationally activated rsr1val12, to serve as a multicopy suppressor of cdc24, indicating that Bud5p functions as a GDS for Rsr1p in vivo. To identify the GAP (GTPase-activating protein) for Rsr1p, a genetic selection was designed based on the observation that mutationally activated rsr1val12, but not wild-type RSR1, can serve as a multicopy suppressor of yeast RAS2(Ts) mutants. Mutants were selected that allowed wild-type RSR1 to act as a multicopy suppressor of RAS2(Ts). Two such mutations proved to be in the BUD2 gene, suggesting that Bud2p functions as a GAP for Rsr1p in vivo.
authors.affiliation: Department of Biology, Indiana University, Bloomington 47405.
authors.forename: A
authors.initials: A
authors.lastname: Bender
mesh_terms: D018797:Cell Cycle Proteins; D020558:GTP Phosphohydrolases / Q000096:biosynthesis* / Q000235:genetics; D005800:Genes, Fungal; D020662:Guanine Nucleotide Exchange Factors; D000072235:Mating Factor; D010455:Peptides / Q000235:genetics; D010675:Pheromones / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D013489:Suppression, Genetic; D020691:rab GTP-Binding Proteins
chemical_list: C073594:CDC24 protein, S cerevisiae; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D010455:Peptides; D010675:Pheromones; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D000072235:Mating Factor; D020558:GTP Phosphohydrolases; C084013:RSR1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins