GLUTATHIONE TRANSFERASE GENE FAMILY FROM THE HOUSEFLY MUSCA-DOMESTICA

Three new glutathione transferase (GST) genes from the housefly Musca domestica are described. These genes, identified as MdGST-2, -3, and - 4, were from cDNA clones obtained from a cDNA bank in phage lambda. Th e bank was prepared using poly(A)(+) RNA from a housefly that is highl y resistant to organophosphate insecticides because of enhanced expres sion of multiple members of the glutathione transferase gene family. T he DNA sequence of each is reported and has a complete open reading fr ame that specified an amino acid sequence similar to other dipteran gl utathione transferases. Based on phylogenetic analysis, we can conclud e that the insect glutathione transferase gene family falls into two g roups, each of which evolves at a different rate, presumably due to di fferences in functional constraints. We show that MdGST-1 (and their h omologues from Drosophila and Lucilia) evolve at a significantly slowe r rate than the other members of the gene family. Each house fly GST c DNA was inserted into a bacterial plasmid expression system and a glut athione transferase activity was expressed in Escherichia coli. The tr anscription pattern of each of these glutathione transferases was exam ined in a variety of different housefly strains that are known to diff er in their resistance to organophosphate insecticides due to differen t patterns of glutathione transferase expression. We found that the le vel of transcription for two of our clones was positively correlated w ith the level of organophosphate resistance.