Molecular dissection of the 5 ' region of no-on-transientA of Drosophila melanogaster reveals cis-regulation by adjacent dGpi1 sequences

The nonA gene of Drosophila melanogaster is important for normal vision, co urtship song, and viability and lies similar to 350 bp downstream of the dG pi1 gene. Full rescue of nonA mutant phenotypes can be achieved by transfor mation with a genomic clone that carries similar to2 kb Of 5' regulatory ma terial and that encodes most of the coding sequence of dGpi1. We have analy zed this 5' region by making a series of deleted fragments, fusing them to yeast GAL4 sequences, and driving UAS-nonA expression in a mutant nonA back ground. Regions that both silence and enhance developmental tissue-specific expression of nonA and that are necessary for generating optomotor visual responses are identified. Some of these overlap the dGpi1 sequences, reveal ing cia-regulation by neighboring gene sequences. The largest 5' fragment w as unable to rescue the normal electroretinogram (ERG) consistently, and no rescue at all was observed for the courtship song phenotype. We suggest th at sequences within the nonA introns that were missing in the UAS-nonA cDNA may carry enhancer elements for these two phenotypes. Finally, we speculat e on the striking observation that some of the cis-regulatory regions of no nA appear to be embedded within the coding regions of dGpi1.