Two classes of dominant inhibitory ras mutants have been characterized, one that interferes with the function of Ras proteins of proto-oncogenes much more strongly than oncogenic Ras, and another that inhibits both forms of Ras function. Studies in this laboratory have identified a 116Y mutant (v-Ha-ras N116Y) that appears to belong to the former class. This mutant induced a revertant phenotype much more strongly in cells transformed by the Ha-ras proto-oncogene than the activated oncogenes. NIH3T3 cells expressing 116Y were resistant to transformation by retroviruses carrying v-abl and v-fes tyrosine kinase oncogenes, which required cellular Ras activities, but not by v-ras oncogene viruses. Chimeric 116Y mutants have been constructed between Ha-ras and Ki-ras involving exchange of the highly- conserved GTP-binding domain and the hypervariable C-terminal membrane-binding domain, in order to study the function of these variables. These inhibitory ras mutants have been employed to study cellular signalling pathways that are directly mediated by cellular Ras function.
