Interaction between the Saccharomyces cerevisiae CDC25 gene product and mammalian ras

In order to characterize the interaction between the Saccharomyces cerevisiae Cdc25 protein and Harveyras (p21^H-ras), we have constructed a yeast strain disrupted at the RAS1 and RAS2 loci, expressing both p21^H-ras and tne catalytic domain of the bovine GTPase activating protein (GAP) and containing the cdc25-2 mutation. Such a strain exhibits a temperature-sensitive phenotype. The shift to the nonpermissive temperature is accompanied by the loss of guanyl nucleotide-dependent activity of adenylylcyclase in vitro. The temperature-sensitive phenotype can be rescued by CDC25 itself, as well as by a plasmid containing a truncated SDC25 gene. In addition, wild type CDC25 significantly improves the guanyl nucleotide response observed in the background of the cdc25^ts allele at the permissive temperature in a dosage-dependent manner and restores the guanyl nucleotide response at the restrictive temperature. Both CDC25 and a truncated SDC25 also restored p21^H-ras-dependent guanyl nucleotide response in a strain isogenic to the one described above but containing a disrupted CDC25 locus instead of the temperature-sensitive allele. These results suggest that the S. cerevisiae Cdc25 protein interacts with p21^H-ras expressed in yeast by promoting GDP-GTP exchange. It follows that the yeast system can be used for characterizing the interaction between guanyl nucleotide exchangers of Ras proteins and mammalian p21^H-ras.