Guanyl nucleotide-binding proteins (GNPs) are involved in the regulation of receptor mediated transmembrane signal transduction. The retinal photon receptor, rhodopsin, is linked to a cGMP phosphodiesterase by the GNP, transducin (Gt). Stimulatory and inhibitory receptors of the adenylate cyclase system are coupled to the catalytic subunit through two GNPs, Gs and Gi, respectively. A fourth GNP, Go, functionally interacts with muscarinic receptors and rhodopsin; however, its physiological function is unclear. All of these GNPs exhibit functional similarities and structurally are composed of alpha, beta, and gamma, subunits. A number of cDNA clones have been isolated from a bovine retinal library and one (gamma Go9) has been sequenced in its entirety with the deduced amino acid sequences corresponding to Go alpha. Other clones appear to be related to but not necessarily identical to gamma Go9. Additionally, a bovine genomic DNA library was screened using the Go alpha cDNA, gamma Go9, as a probe. A number of clones of varying intensities of hybridization have been isolated and purified. Restriction analysis and hybridization with various probes corresponding to different regions of the cDNA have revealed that at least three related but different clones have been identified.
