Expression of normal and activated human Ha-ras cDNAs in Saccharomyces cerevisiae

We expressed normal and activated human cellular Ha-ras cDNAs which encode 21,000-dalton polypeptides (p21s) in Saccharomyces cerevisiae by their insertion into a 2 micron-based replicating plasmid vector under 3-phosphoglycerate kinase promoter control. We found that newly synthesized p21 in S. cerevisiae was produced as a soluble precursor (pro-p21) which matured into a form electrophoretically indistinguishable from the processed form (p21) observed in mammalian cells. Coincident with the processing event was translocation to a membrane component, suggesting a coupling of the two events. Using vectors that direct the synthesis of p21 variants possessing the ability to autophosphorylate in vitro, we found that processing of p21 did not significantly affect this autophosphorylation reaction. In contrast to Escherichia coli, marked phenotypic changes were observed in S. cerevisiae as a consequence of the synthesis of p21, including reduction in growth rate and induction of flocculation. Accompanying these phenotypic alterations was a significant elevation of adenylate cyclase activity.