An analysis of two tandem promoters of the Drosophila purple gene

We have analyzed two tandem promoters, separated by only about 400 bp, of t he purple (pr) gene of Drosophila malanogaster, by fusing them to the firef ly luciferase reporter gene and employing a transient expression assay with Drosophila S2 cells. Both the distal promoter and the proximal promoter we re found to function in S2 cells and an about 700 bp long region (-270 to 421), containing both promoters, was sufficient to effect maximal promoter activity, When the two promoters were analyzed separately, the distal promo ter was found to be much stronger in its function than the proximal promote r. At least three different kinds of cis elements near the transcription st art site appear to play crucial roles in driving constitutive expression fr om the distal promoter. On the other hand, only a single cia element, which may play a role in tissue-specific expression, appears to be important for the activity of the proximal promoter in S2 cells. We propose that the clu stering of important cis elements near the transcription start sites may be responsible for the selective regulation of the two tandem promoters.