The function of ras genes in: Saccharomyces cerevisiae

This chapter describes the function of RAS genes in the yeast Saccharomyces cerevisiae and the components of the pathway in which it acts. Yeast RAS proteins share considerable homology with the mammalian RAS proteins. A short sequence including an invariant cysteine residue is always found at the carboxyl end of all RAS proteins. Deletion of either RAS1 or RAS2 alone has no deleterious effects on the growth of yeast strains in rich media, while deletion of both the genes is lethal. This shows that RAS1 and RAS2 are functionally interchangeable for growth in rich medium. Purified adenylate cyclase can be stimulated by purified RAS protein in vitro. The purified RAS2 protein can be phosphorylated in vitro by mammalian A kinase and the phosphorylated RAS protein is ∼2-fold less active in stimulating adenylate cyclase in vitro than is dephosphorylated protein. In addition, both RAS1 and RAS2 proteins are phosphorylated in vivo.