Transcriptional analysis of the Drosophila GABA receptor gene resistance to dieldrin.

The Resistance to dieldrin (Rdl) gene encodes a novel subunit of a gamma-aminobutyric acid (GABA)-gated chloride ion channel in Drosophila. We were interested in defining the spatial and temporal expression pattern of this gene and in understanding the basis of its regulation. Rdl is expressed in both the embryonic central and peripheral nervous system. Here, we describe the complete Rdl transcription unit (approximately 50 kb) via localization of the flanking transcripts. The Rdl transcript itself is large (8.8 kb) and is composed of a short open reading frame (2 kb) with exceptionally long 5' (1.8-kb) and 3' (5-kb) untranslated regions (UTRs). The correct spatial and temporal expression of Rdl can be rescued by transformation constructs containing only 3.5 kb of DNA, a region which encompasses the transcription start point (tsp). This region also contains sequences strikingly similar to those found in other ion channel gene promoters. Failure of minigene constructs lacking the long 3' UTR to fully rescue both the lethal and resistance phenotypes associated with the Rdl locus might arise owing to the role of these sequences in message stability or trafficking.