Characterization of synthetic-lethal mutants reveals a role for the Saccharomyces cerevisiae guanine-nucleotide exchange factor Cdc24p in vacuole function and Na+ tolerance.
Cdc24p is the guanine-nucleotide exchange factor for the Cdc42p GTPase, which controls cell polarity in Saccharomyces cerevisiae. To identify new genes that may affect cell polarity, we characterized six UV-induced csl (CDC24 synthetic-lethal) mutants that exhibited synthetic-lethality with cdc24-4ls at 23 degrees. Five mutants were not complemented by plasmid-borne CDC42, RSR1, BUD5, BEM1, BEM2, BEM3 or CLA4 genes, which are known to play a role in cell polarity. The csl3 mutant displayed phenotypes similar to those observed with calcium-sensitive, Pet- vna mutants defective in vacuole function. CSL5 was allelic to VMA5, the vacuolar H(+)-ATPase subunit C, and one third of csl5 cdc24-4ls cells were elongated or had misshapen buds. A cdc24-4ls delta vma5::LEU2 double mutant did not exhibit synthetic lethality, suggesting that the csl5/vma5 cdc24-4ls synthetic-lethality was not simply due to altered vacuole function. The cdc24-4ls mutant, like delta vma5::LEU2 and csl3 mutants, was sensitive to high levels of Ca2+ as well as Na+ in the growth media, which did not appear to be a result of a fragile cell wall because the phenotypes were not remedied by 1 M sorbitol. Our results indicated that Cdc24p was required in one V-ATPase mutant and another mutant affecting vacuole morphology, and also implicated Cdc24p in Na+ tolerance.
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Department of Microbiology and Molecular Genetics, Markey Center for Molecular Genetics, University of Vermont, Burlington 05405, USA.
Johnson
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D002122:Calcium Chloride / Q000494:pharmacology; D002262:Carboxy-Lyases / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology*; D016764:Cell Polarity / Q000235:genetics; D003433:Crosses, Genetic; D005800:Genes, Fungal / Q000502:physiology; D005804:Genes, Lethal / Q000502:physiology; D005816:Genetic Complementation Test; D020662:Guanine Nucleotide Exchange Factors; D009154:Mutation / Q000502:physiology*; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D006180:Proton-Translocating ATPases / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000187:drug effects / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012965:Sodium Chloride / Q000494:pharmacology*; D025262:Vacuolar Proton-Translocating ATPases; D014617:Vacuoles / Q000502:physiology*
C073594:CDC24 protein, S cerevisiae; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D012965:Sodium Chloride; D025262:Vacuolar Proton-Translocating ATPases; D006180:Proton-Translocating ATPases; D002262:Carboxy-Lyases; C022378:phosphoribosylaminoimidazole carboxylase; D002122:Calcium Chloride