Drosophila Cyclodiene Resistance Gene Shows Conserved Genomic Organization with Vertebrate ?-Aminobutyric AcidAReceptors

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Abstract
Genomic clones from the Rdl locus of Drosophila, whose mutant phenotype is resistant to cyclodiene insecticides and picrotoxin, were characterized by restriction mapping and partial sequencing to determine intron/exon structure. The coding region of the gene comprises nine identified exons and spans >25 kb of genomic DNA. The structure of the Drosophila Rdl receptor subunit was compared with those of vertebrate γ‐aminobutyric acid subtype A (GABAA) receptors and nicotinic acetylcholine receptors (nAChRs). The first six introns in Rdl show positions similar to those in vertebrate GABAA receptors, whereas the last two differ. It is interesting that the last intron appears to be in a position similar to that in nAChRs. These results are examined in relation to the proposal, based on amino acid identities, that Rdl codes for a novel class of GABAA receptor subunit more closely related to glycine receptors, and the possible place ofRdl in the lineage of the receptor superfamily is discussed.