Abstract
The Adh-2 gene of Drosophila mulleri is expressed in the larval fat body and the adult fat body and hindgut, and a 1500-bp element located 2-3 kb upstream of the Adh-2 promoter is necessary for maximal levels of transcription. Previous work demonstrated that deletion of sequences between this upstream element and the Adh-2 promoter results in Adh-2 gene expression in a novel larval tissue, the middle midgut. In this study we show that the upstream element possesses all of the characteristics of a transcriptional enhancer: its activity is independent of orientation, it acts on a heterologous promoter, and it functions at various positions both 5' and 3' to the Adh-2 gene. Full enhancer function can be localized to a 750-bp element, although other regions possess some redundant activity. The ectopic expression pattern is dependent on the proximity of at least two sequence elements. Thus, tissue-specific transcription can involve complex proximity-dependent interactions among combinations of regulatory elements.
