Abstract
Drosophila melanogaster contains two genes encoding glyceraldehyde-3-phosphate dehydrogenase, Gapdh-1 and Gapdh-2. The two genes are highly conserved in their coding sequences but not in their noncoding and flanking sequences. We report that both genes are expressed at higher levels in larval, late pupal, and adult stages than in embryonic, early, and midpupal stages. However, a major difference in the expression of the two genes is observed in the adult stage, during which the level of the Gapdh-1 transcript decreases over fourfold, while that of the Gapdh-2 transcript remains at a constant high level. In addition, the Gapdh-1 transcript appears highly enriched in the thorax section compared with the head and abdomen sections, while the Gapdh-2 transcript is evenly distributed. Analyses of the expression patterns of the two Gapdh hybrid genes, GAP1/2 and GAP2/1, revealed that the two genes have a distinct organization of their regulatory sequences. The principle regulatory sequences of Gapdh-2 reside upstream of the translation start, while the principle sequences specifying the level and developmental pattern of Gapdh-1 expression reside downstream of the translation start.
