Molecular analysis of the structure, organization and expression of the Drosophila G protein ℓ-subunit gene

The present study was undertaken to identify and characterize a gene which is expressed in the nervous system of Drosophila. Since adult head of the fly is enriched with neural tissues, a genomic clone 536, containing a gene predominantly expressed in the head of Drosophila melanogaster was characterized. DNA sequencing showed that a gene present in this clone encodes a protein similar to mammalian G protein γ subunits. G proteins are heterotrimeric, GTP-binding proteins which mediate transduction of extracellular stimuli to intracellular effector molecules. The putative Drosophila γ- subunit (DGγ1) protein shares 46, 43, and 28% identity and 59, 52, and 60% similarity with the γ2, γ3 and γt subunits of the bovine G proteins, respectively. The D-Gγ1 gene produces 2.6-, 1.3-, and 1.1-kb mRNAs which show differential expression pattern but encodes the same D-Gγ1 protein. In situ hybridization and RNA blot analyses showed that (1) the 2.6- kb RNA is expressed only in the central nervous system; (2) the 1.1-kb RNA is expressed in all cells but the highest level is found in the central nervous system; and (3) the 1.3-kb RNA is expressed only in the ovary. In embryos, the 1.1-kb D-Gγ1 RNA is the predominant mRNA species. Structure and organization study of the D-Gγ1 gene demonstrated that two exons and one intron are present in the D-Gγ1 gene and the transcription start site of all three D-G7I mRNAs is the same. The putative promoter region of D-Gyl gene possesses sequences similar to the GC-box but no TATA-box was found. The 3'-untranslated regions of the D-Gγ1 mRNAs vary due to differential utilization of polyadenylation signals. Also, the 5'-untranslated region of the ovary-specific 1.3-kb RNA has an extra 188 nucleotide sequence which originates by alternative splicing. The present study has indicated that D-Gγ1 gene is expressed predominantly in neural tissues and may play important role in neuronal transduction processes. The size differences in the 5'- and 3'-untranslated regions of the D-Gγ1 mRNAs may regulate translatability and differential expression of the D-Gγ1 gene.