A KP element inserted between the two promoters of the alcohol dehydrogenase gene of Drosophila melanogaster differentially affects expression in larvae and adults

An allele of the Drosophila melanogaster alcohol dehydrogenase (Adh) gene has a 1.15-kb KP element inserted, in the same orientation as Adh transcription, five nucleotides upstream of the distal transcription start site. The target site - GTCCAAGT - in Adh between nucleotides -13 and -6 is duplicated at both ends of the insertion. Adult flies with either one or two copies of the allele have less than 12% of the alcohol dehydrogenase (ADH) activity of the controls. Activity levels are also reduced in larvae, but by a much smaller amount. Quantitative Northern analyses showed that the low activity level in adults was caused by reduced transcript levels from the distal promoter. 5' RACE experiments indicated that adult transcripts were mostly initiated downstream of the distal promoter but some skipped the first adult exon. In late third-instar larvae the transcripts present were from the proximal promoter. After the KP element was deleted by an appropriate breeding program, the distal transcript increased in adults to the control level, but ADH activity increased to only 50% of the control. No nucleotide changes were found in the gene that could explain this difference.