Diversification of Drosophila chloride channel gene by multiple posttranscriptional mRNA modifications

We have identified and analyzed a Drosophila melanogaster gene that encodes a chloride channel subunit (DrosGluCl-alpha) previously shown to function as a glutamate-gated chloride channel in an in vitro expression system. Seq uence analysis of several cDNAs corresponding to the gene revealed sequence diversity in their open reading frames at seven specific sites. Site-speci fic A-to-G variations between cDNA and genomic sequences, consistent with R NA editing, were detected at five nucleotide positions. In addition, sequen ce variations among cDNA clones consistent with alternative splicing of mRN A were found at two different sites. In the 5' region, two small adjacent e xons, containing similar but distinct modular sequences, are alternatively incorporated into the mature mRNA. In the 3' region, alternative splicing g enerates a variant encoding a protein with four additional amino acids just upstream of the fourth transmembrane domain. Combinations of RNA editing a nd alternative splicing can lead to extensive diversification of transcript s. These results give the first example of RNA editing in neurotransmitter- gated chloride channel genes or of alternative splicing in a glutamate-gate d chloride channel gene of Drosophila.