Structure of two unlinked Drosophila melanogaster glyceraldehyde-3-phosphate dehydrogenase genes.

Two Drosophila genes that code for the enzyme glyceraldehyde-3-phosphate dehydrogenase (Gapdh) have been isolated and their structures determined by DNA sequence analysis. The two genes, Gadph-1 and Gapdh-2, are homologous to each other in their coding regions but differ entirely in the 5' and 3' flanking regions. Both genes are functionally expressed in adult flies as determined by Northern blot analysis using gene-specific probes. Gapdh-1 is mapped by in situ hybridization at position 43E-F on the right arm of the second chromosome and Gapdh-2 at position 13F on the left arm of the X chromosome. Transcription initiation sites as well as polyadenylation sites for both Gapdh transcripts have also been determined. Gapdh-1 lacks a sequence homologous to the TATA box in its -30-base pair region that is characteristic of many RNA polymerase II transcribed promoters. In contrast, Gapdh-2 contains a consensus TATA box sequence as well as a CAAT box in its promoter region. Furthermore, a sequence element ATTTGCAT (dc) and nontandem multiple direct repeats have been found in the -35 to -155-base pair 5' flanking region. Other than the intron located in the 5' noncoding region of Gapdh-2, both genes lack intervening sequences.