Genetic analysis of yeast RAS1 and RAS2 genes

We present a genetic analysis of RAS1 and RAS2 of S. cerevisiae, two genes that are highly homologous to mammalian ras genes. By constructing in vitro ras genes disrupted by selectable genes and introducing these by gene replacement into the respective ras loci, we have determined that neither RAS1 nor RAS2 are by themselves essential genes. However, rasl − ras2 − spores of doubly heterozygous diploids are incapable of resuming vegetative growth. We have determined that RAS1 is located on chromosome XV, 7 cM from ade2 and 63 cM from his3; and RAS2 is located on chromosome XIV, 2 cM from met4. We have also constructed by site-directed mutagenesis a missense mutant, RAS2 val19, which encodes valine in place of glycine at the nineteenth amino acid position, the same sort of missense mutation that is found in some transforming alleles of mammalian ras genes. Diploid yeast cells that contain this mutation are incapable of sporulating efficiently, even when they contain wild-type alleles.