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Go, a guanine nucleotide binding protein found predominantly in neural tissues, interacts in vitro with rhodopsin, muscarinic, and other receptors and has been implicated in the regulation of ion channels. Despite the virtual identity of reported cDNA sequences for the alpha subunit of Go (Go alpha), multiple molecular weight forms of mRNA have been identified in tissues from all species examined. To investigate the molecular basis for the size heterogeneity of Go alpha mRNAs, four cDNA clones were isolated from the same retinal lambda gt10 cDNA library that was used earlier to isolate lambda GO9, a clone encompassing the complete coding region of Go alpha. These clones were identified as Go alpha clones based on nucleotide sequence identity with lambda GO9 in the coding region; they diverge, however, from lambda GO9 in the 3'-untranslated region 28 nucleotides past the stop codon. An oligonucleotide probe complementary to a portion of the 3'-untranslated region of lambda GO9 that differs from the newly isolated clones hybridized with 3.0- and 4.0-kb mRNAs present in bovine brain and retina whereas a similar probe for the unique region of the new clones hybridized with a 4.0-kb mRNA in both tissues and with a 2.0-kb mRNA found predominantly in retina. A similar hybridization pattern was observed when brain poly(A+) RNA from other species was hybridized with the different 3'-untranslated region probes. It appears that differences in the 3'-untranslated regions could, in part, be the basis for the observed heterogeneity in Go alpha mRNAs.

Go alpha is a 39-kDa guanine nucleotide-binding protein (G protein) similar in structure and function to Gs alpha and Gi alpha of the adenylate cyclase complex and to transducin (Gt alpha) of the retinal photon receptor system. Although expression of Go alpha protein has been reported to be tissue-specific, other workers have found Go alpha mRNA in all rat tissues examined. In order to clarify this contradiction, studies to verify the distribution of Go alpha mRNA and protein in bovine and rat tissues were performed. Tissues were screened for the presence of Go alpha mRNA by use of a series of restriction fragments of a bovine retinal cDNA clone, lambda GO9, and oligonucleotide probes complementary to sequences specific among G alpha subunits for the 5' untranslated and coding regions of Go alpha. These probes hybridized predominantly with mRNA of 4.0 and 3.0 kb in bovine brain and retina. A 2.0-kb mRNA in retina also hybridized strongly with the cDNA but weakly with the oligonucleotide probes. In bovine lung, two mRNAs of 1.6 and 1.8 kb hybridized with the cDNA while only the 1.6-kb species hybridized with the coding-region oligonucleotide. In bovine heart, only a 4.0-kb mRNA was detected and in amounts much less than those in the other tissues. A similar distribution of Go alpha mRNAs was seen in rat tissues. In bovine tissues, Go alpha protein was identified with rabbit polyclonal antibodies directed against purified bovine brain Go alpha. An immunoreactive 39-kDa membrane protein was found principally in retina and brain, and in a lesser amount in heart.(ABSTRACT TRUNCATED AT 250 WORDS)