Transcriptional control of Ca2+-activated K+ channel expression: Identification of a second, evolutionarily conserved, neuronal promoter

Neuronal signaling properties are largely determined by the quantity and co mbination of ion channels expressed. The Drosophila slowpoke gene encodes a Ca2+-activated K+ channel used throughout the nervous system. The slowpoke transcriptional control region is large and complex. To simplify the searc h for sequences responsible for tissue-specific expression, we relied on ev olutionary conservation of functionally important sequences. A number of co nserved segments were found between two Drosophila species. One led us to a new 5' exon and a new transcriptional promoter: Promoter C0. In larvae and adults, Promoter C0 was demonstrated to be neural-specific using flies tra nsformed with reporter genes that either contain or lack the promoter, The transcription start site of Promoter C0 was mapped, and the exon it appends to the 5' end of the mRNA was sequenced, This is the second neural-specifi c slowpoke promoter to be identified, the first being Promoter C1. Promoter choice does not alter the encoded polypeptide sequence, RNAase protection assays indicate that Promoter C0 transcripts are approximately 12 times mor e abundant that Promoter C1 transcripts. Taken together, these facts sugges t that promoter choice may be a means for cells to control channel density.