Abstract
A G protein alpha subunit gene has been isolated from a Drosophila melanogaster genomic library using a combination of bovine rod and cone transducin alpha subunit cDNAs as a probe under reduced stringency conditions. The gene, DG alpha 1, encodes a protein with an amino acid sequence 78% identical to bovine Gi alpha 1. However, unlike all reported Gi alpha subunit the DG alpha 1-encoded protein is not expected to be a pertussis toxin substrate, because it lacks a cysteine at the appropriate site. The protein coding region of the gene is split by four introns. The sequence of a head tissue cDNA clone, as well as amino acid similarities to mammalian G proteins, confirms this exon/intron structure. Northern blots of total cellular RNA reveal a major 2.3-kilobase transcript and a less abundant 1.7-kilobase transcript. These transcripts are most abundant in RNA from embryos and pupae. The DG alpha 1 gene is located on band 65C on the left arm of the third chromosome, on the basis of in situ hybridizations to Drosophila salivary gland polytene chromosomes.
Highlights
A G protein a subunit gene has been isolated from a subunit binds GTP, dissociates from the @ycomplex, and Drosophila melanogastergenomiclibrary using a com- interacts directly with an effector enzyme
Much of the biochemical characterization of G proteins has focused on vertebrate signal transduction systems
We describe here the isolation and characterization of a gene encoding a D. melanogaster G proteina subunit
Summary
A D. nelanogaster genomic library was screened with bovine transducin cDNA clones at reduced stringency- Fourteen positively hybridizing plaques were isolated from the initial screening. The sequences of the protein coding regions of the gene and the adult head cDNA (Fig. 2) were identical save for one base difference. The one base difference in the protein coding region may be either a cloning artifact or a strain polymorphism, since a different cDNA, isolated from a 0-3 h Drosophila Oregon R strain embryo cDNA library, is identical to the gene at base 8 but differs at bases 177 and 751 (datanot shown). A comparison of the proteins encoded by DGal and Gia cDNAs derived from three different mammalian genes (Fig. 3 B ) reveals the highest degree of amino acid identity between DGa1 and bovine Gial. Seventy-eight percent of the corresponding amino acids in DGal and Gial are identical Despite this highdegree of similarity, there is a major difference between the DGal gene product and mammalian Gias. All mammalian Gias contain a cysteine 4 residues from the carboxyl terminus which serves as a substrate
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