Doctoral Dissertations

Kausik Ray

Date of Award

5-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Life Sciences

Major Professor

Ranjan Ganguly

Committee Members

Mary Ann Handel, Bruce McKee, David Brian

Abstract

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.

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