TRANSCRIPTIONAL ANALYSIS OF THE DROSOPHILA GABA RECEPTOR GENE RESISTANCE TO DIELDRIN

The Resistance to dieldrin (Rdl) gene encodes a novel subunit of a gam ma-aminobutyric acid (GABA)-gated chloride ion channel in Drosophila. We were interested in defining the spatial and temporal expression pat tern of this gene and in understanding the basis of its regulation. Rd l is expressed in both the embryonic central and peripheral nervous sy stem. Here, we describe the complete Rdl transcription unit (approxima te to 50 kb) via localization of the banking transcripts. The Rdl tran script itself is large (8.8 kb) and is composed of a short open readin g frame (2 kb) with exceptionally long 5' (1.8-kb) and 3' (5-kb) untra nslated regions (UTRs). The correct spatial and temporal expression of Rdl can be rescued by transformation constructs containing only 3.5 k b of DNA, a region which encompasses the transcription start point (ts p). This region also contains sequences strikingly similar to those fo und in other ion channel gene promoters. Failure of minigene construct s lacking the long 3' UTR to fully rescue both the lethal and resistan ce phenotypes associated with the Rdl locus might arise owing to the r ole of these sequences in message stability or trafficking. (C) 1998 J ohn Wiley & Sons, Inc.