Heterotrimeric G proteins function to relay information from cell surface receptors to intracellular effectors (1). Each of a very broad range of receptors specifically detects an extracellular stimulus (a photon, pheromone, odorant, hormone or neurotransmitter) while the effectors (e.g., adenyl cyclase), which act to generate one or more intracellular messengers, are less numerous. In mammals, G protein alpha, beta and gamma polypeptides are encoded by at least 16, 4 and 7 genes, respectively (2-5). Most interest in G proteins has been focused on their alpha subunits, since these proteins bind and hydrolyze GTP and most obviously regulate the activity of the best studied effectors. More recent evidence, however, has established an important regulatory role for the beta gamma subunits (6-8). The Gs subfamily of G alpha subunits includes two closely related proteins, Ga s and Ga olf, which respectively stimulate adenylate cyclase and mediate response to olfactory stimuli (9).