Structural changes in the promoter region mediate transvection at the sn-glycerol-3-phosphate dehydrogenase gene of Drosophila melanogaster

Trans effects at the sn-glycerol-3-phosphate dehydrogenase locus (Gpdh) of Drosophila melanogaster give rise to an increase in GPDH activity and mRNA from the wild-type allele in heterozygotes with some low-activity alleles. Either the low-activity alleles that induce the effect have a defective P-e lement inserted between the promoter and a downstream intronic enhancer ele ment or the promoter region is deleted. The trans effect is pairing depende nt, characteristic of transvection at some other loci. The defective P-elem ents that mediate transvection are located between the promoter and at leas t up to 6 bp downstream of the transcription start site. Transvection at Gp dh appears similar to the "enhancer action in trans" mode at the yellow loc us.