FUNCTION OF YEAST ONCOGENE HOMOLOGUES

There are two genes, RAS1 and RAS2, in the yeast Saccharomyces cerevisiae that share extensive homology with each other and with the human proto-oncogene family c-ras. We will conduct a genetic and physiologic study of the yeast RAS1 and RAS2 genes in order to determine the role these genes play in the normal growth of a single eucaryotic cell. It is anticipated that results from these studies will yeild insight into the role c-ras genes play in higher eucaryotic cells and suggest some mechanisms by which single amino acid changes in those genes can result in proliferative transformation. In preliminary studies we have defined a number of phenotypes associated with specific mutant alleles of RAS1 and RAS2. Strains lacking both RAS genes (ras1[unreadable]-[unreadable] ras2[unreadable]-[unreadable]) are nonviable. Strains containing mutant RAS alleles consisting of single amino acid mutations analogous to the transformation-activating alleles of human c-ras are viable. However, they show a number of altered phenotypes: they display a dominant deficiency in sporulation (Spo[unreadable]-[unreadable]); they fail to arrest uniformly at the beginning of the cell cycle when starved for various nutrients; they show a substantial reduction in viability upon starvation; and, they fail to accumulate glycogen and trehalose. Finally, increased expression of these mutant alleles causes lethality. We plan to assess the interrelations between the RAS system and cAMP-mediated growth regulation through specific constructions and genetic physiological studies. We will evaluate the structure and functions of RAS1 through identification and characterization of ts-lethal and Spo[unreadable]-[unreadable] alleles of the gene following site-directed mutagenesis. We will define those components that physically interact with the RAS proteins through biochemical cross-linking studies and through isolation of allele-specific suppressors of various RAS mutations. Finally, we hope to identify both additional components of the RAS system and possible alternative regulatory pathways by isolating and characterizing allele-non-specific suppressors of various RAS mutants. (X)