Interactions between adenylate cyclase and the yeast GTPase-activating protein IRA 1

The adenylate cyclase system of the yeast Saccharomyces cerevisiae contains many proteins, including the CYR1 polypeptide, which is responsible for catalyzing the formation of cyclic AMP from ATP, RAS1 and RAS2 polypeptides, which mediate stimulation of cyclic AMP synthesis by guanine nucleotides, and the yeast GTPase-activating protein analog IRAl. We have previously reported that adenylate cyclase is only peripherally bound to the yeast membrane. We have concluded that IRAl is a strong candidate for a protein involved in anchoring adenylate cydase to the membrane. We base this conclusion on the following criteria: (i) a disruption of the IRA] gene produced a mutant with very low membrane-associated levels of adenylate cyclase activity, (ii) membranes made from these mutants were incapable of binding adenylate cyclase in vitro, (iii) IRAl antibodies inhibit binding of adenylate cyclase to the membrane, and (iv) IRAl and adenylate cyclase comigrate on Sepharose 4B. Ras proteins in the yeast Saccharomyces cerevisiae share many similarities to the mammalian p2lras proto-oncogene products. Both yeast and mammalian Ras proteins share structural homology with the other members of the large family of GTP-binding proteins that includes the G proteins