Muscle-specific transcriptional regulation of the slowpoke Ca2+-activated K+ channel gene

Transcriptional regulation of the Drosophila slowpoke calcium-activated pot assium channel gene is complex. To date, five transcriptional promoters hav e been identified, which are responsible for slowpoke expression in neurons , midgut cells, tracheal cells, and muscle fibers. The slowpoke promoter ca lled Promoter C2 is active in muscles and tracheal cells. To identify seque nces that activate Promoter C2 in specific cell types, we introduced small deletions into the slowpoke transcriptional control region. Using transform ed flies, we asked how these deletions affected the in situ tissue-specific pattern of expression. Sequence comparisons between evolutionarily diverge nt species helped guide the placement of these deletions. A section of DNA important for expression in all cell types was subdivided and reintroduced into the mutated control region, a piece at a time, to identify which porti on was required for promoter activity. We identified 55-, 214-, and 20-nucl eotide sequences that control promoter activity. Different combinations of these elements activate the promoter in adult muscle, larval muscle, and tr acheal cells.