MOLECULAR-CLONING OF AN ALPHA-ESTERASE GENE-CLUSTER ON CHROMOSOME 3R OF DROSOPHILA-MELANOGASTER

All or part of the alpha-esterase gene cluster in Drosophila melanogas ter has been isolated by screening a YAC clone that spans cytological region 84D3-10 with consensus carboxyl/cholinesterase oligonucleotides . The cluster encompasses 11 putative esterase genes within 65 kb of g enomic DNA and is one of the largest clusters of related protein-codin g genes yet reported in Drosophila. The cluster must include the gene encoding the major alpha-esterase isozyme, EST9, which has previously been mapped to 84D3-5. It probably also includes the genes encoding th e EST23, MCE and ALI esterases that have previously been mapped to 84D 3-E2. The latter three are homologs of genes involved in organophospha te insecticide resistance in the sheep blowfly, Lucilia cuprina and th e housefly, Musca domestica, Sequencing of one of the putative esteras e genes in the Drosophila cluster, alpha E1, shows that it would encod e features characteristic of an active carboxyl/cholinesterase, includ ing the so-called catalytic triad, the nucleophilic elbow and oxyanion hole. It also shows that the closest relative of alpha E1 amongst pre viously published esterase sequences is ESTB1, which confers organopho sphate resistance in Culex mosquitoes, We argue that we have cloned th e D. melanogaster version of a major cluster of esterase genes which h ave variously mutated to confer organophosphate resistance in diverse Diptera.