RAS2 of Saccharomyces cerevisiae is required for gluconeogenic growth and proper response to nutrient limitation

Abstract

Saccharomyces cerevisiae contains two genes with remarkable homology to members of the ras oncogene family. These two genes, RAS1 and RAS2, constitute an essential gene family since spores with disruptions of both genes fail to grow. We report here that strains containing RAS2 disruptions have three distinct phenotypes. First, they fail to grow efficiently on nonfermentable carbon sources. Second, they hyperaccumulate the storage carbohydrates glycogen and trehalose. Third, diploid cells homozygous for the RAS2 disruptions sporulate on rich media. Extragenic suppressors have been isolated that suppress the gluconeogenic defect. These suppressors fall into at least three complementation groups, mutations in two of which bypass the normal requirement of RAS for cell viability, allowing cells containing neither RAS gene to grow. The phenotype of the RAS2 mutant and extragenic suppressors implicate RAS with some function in the normal response to nutrient limitation.