Occurrence in Saccharomyces cerevisiae of a gene homologous to the cDNA coding for the alpha subunit of mammalian G proteins.

From cross-hybridization studies with cDNAs that code for the alpha subunits of rat brain guanine nucleotide-binding regulatory (G) proteins, we have isolated a gene from yeast Saccharomyces cerevisiae encoding an amino acid sequence that is highly homologous to the alpha subunit of the G protein that mediates inhibition of adenylate cyclase (Gi alpha) from rat brain. The gene, tentatively designated as GPA1, contains a contiguous, single open reading frame of 1416 nucleotides that codes for a protein of 472 amino acids with a calculated Mr of 54,075. The predicted amino acid sequence of the protein encoded by the GPA1 gene (tentatively designated as G protein 1 alpha or GP1 alpha) is remarkably homologous to the amino acid sequence of rat brain Gi alpha and the alpha subunit of the G protein of unknown function (Go alpha); the primary structure of the sites for GTP hydrolysis as well as GTP interaction are nearly identical. The main difference in the molecular sizes of yeast GP1 alpha (472 amino acids) and rat brain Gi alpha (355 amino acids) is due to the presence of a stretch of 110 extra amino acid residues in yeast GP1 alpha, which are inserted near the NH2-terminal one-third of mammalian Gi alpha. From blot-hybridization analysis, the size of the GP1 alpha mRNA was estimated as 1.7 kilobases.