Drosophila sn-glycerol-3-phosphate dehydrogenase isozymes are generated by alternate pathways of RNA processing resulting in different carboxyl-terminal amino acid sequences.

J L Cook,G C Bewley,J B Shaffer

doi:10.1016/s0021-9258(18)38049-9

Abstract

Glycerol-3-phosphate dehydrogenase (GPDH, Ec 1.1.1.8) in Drosophila melanogaster consists of a family of three isozymes designated as GPDH-1, 2, and 3 which exhibit a unique temporal and tissue-specific pattern of expression. While each isozyme is encoded by the same structural gene, they differ by the amino acid sequence at the COOH-terminal end, with GPDH-3 having the sequence Asn-His-Pro-Glu-His-Met-COOH and with GPDH-1 extended by the three amino acid sequence Glu-Asn-Leu-COOH. We have isolated both genomic and cDNA clones in order to examine the structure of the 3'-end of this gene and its transcriptional products. This analysis has demonstrated three classes of transcripts, each differing in the 3'-untranslated region and coding for an enzyme with a different COOH-terminal amino acid sequence. Each transcript is shown to arise through the differential expression of three isotype-specific exons at the 3'-end of the gene. We propose a model where the expression of each isotype-specific transcript is controlled through a developmentally regulated process of 3'-end formation and alternate splicing pathways of the pre-mRNA. Furthermore, since each transcript and its cognant isozyme is tissue-specific in expression, this model suggests a role for tissue-specific trans-acting factors in these processing events.

Highlights

Drosophila GPDH Gene StructureTion of acceptor site I1 would result in the excision of a 1073bp intron with the splicing of exon 8 to exon 6
COOH-terminal aminoacid sequence.Each transcript arm of the second chromosome [5]and has been localized to is shown to arise through the differential expression the cytogenetic interval 26A on the basis of deletion mapping of three isotype-specifeixconsat the 3’-endof thegene. [6] and in situhybridization of cloned sequences to polytene
Tion of acceptor site I1 would result in the excision of a 1073bp intron with the splicing of exon 8 to exon 6. This pathway would generate an open reading frame that encodes an additionalthree COOH-terminal amino acids, the sequence of which is identical to GPDH-1(4), followed by a termination codon and four downstream polyadenylation signals at positions 1362,1720,1767, and 1822

Summary

Drosophila GPDH Gene Structure

Tion of acceptor site I1 would result in the excision of a 1073bp intron with the splicing of exon 8 to exon 6 This pathway would generate an open reading frame that encodes an additionalthree COOH-terminal amino acids, the sequence of which is identical to GPDH-1(4), followed by a termination codon and four downstream polyadenylation signals at positions 1362,1720,1767, and 1822. If poly(A) site selection occurs in exon 7, a pre-mRNA would result that required the excision of the 524-bp intron utilizing the internal 5"splice site in exon 6 and acceptor site I. Processing of this transcript would yield an mRNA with a minimal size range of 1.3-1.4 kb. Probe C, which is complementary to the first 20 nucleotides

LA kb

Gln Asn Leu ***

DISCUSSION

Findings

Distance from iunction