title: Molecular cloning and characterization of cDNA encoding the GTP-binding protein alpha i and identification of a related protein, alpha h.
abstract: We have cloned and characterized cDNA encoding alpha i, the GTP-binding subunit of Gi, a protein that mediates hormonal inhibition of adenylate cyclase and hormonal regulation of other membrane functions. We have also identified cDNA encoding a putative protein, which we have named alpha h, that is highly homologous to alpha i but different from other known GTP-binding proteins. Both cDNAs were isolated from a bovine pituitary library. The cDNA encoding alpha i was identified by finding that the amino acid sequence determined for two tryptic peptides from alpha i agreed exactly with amino acid sequences deduced from the cDNA. We also determined the amino acid sequence of peptides derived from alpha o, a related 39-kDa protein purified from bovine brain. These sequences are approximately 75% identical to the sequence determined for alpha i. Southern blot analysis of bovine genomic DNA, using as probes radiolabeled cDNAs for alpha i, alpha h, and the alpha subunit of a related protein, transducin, showed that each probe recognized different genomic DNA fragments. Our results suggest a further level of complexity in the organization of the G-protein gene family, with multiple G proteins of very similar structural properties likely to be identified as products of distinct genes.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000032:analysis*; D019204:GTP-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D012243:Rhodopsin / Q000032:analysis
chemical_list: D000246:Adenosine Diphosphate Ribose; D004247:DNA; D012243:Rhodopsin; D019204:GTP-Binding Proteins