CHARACTERIZATION OF THE ESTP PROTEIN IN DROSOPHILA-MELANOGASTER AND ITS CONSERVATION IN DROSOPHILIDS

The beta-esterase cluster of D. melanogaster comprises two tandemly du plicated genes, Est6 encodes the well-characterized 5' gene, but the p roduct of the second gene, denoted EstP, had not previously been ident ified, Here we show that the EstP gene encodes the carboxylesterase ES T7. Expression of EstP using the Baculovirus system led to production of a carboxylesterase biochemically indistinguishable from EST7. Furth ermore, a naturally occurring EstP variant produces greatly reduced am ounts of EstP mRNA and no detectable EST7 protein. Finally, introducti on of a wild-type copy of EstP by germline transformation into the var iant strain confers the wild-type EST7 phenotype. We show that EST7 di ffers from EST6 in its substrate and inhibitor specificities and tissu e distribution, Germline transformation experiments show that EstP exp ression is controlled by sequences located between 192 bp 5' and 609 b p 3' of the EstP coding region. Data comparisons with other drosophili d esterases suggest that the site of expression, and hence the functio n, of EST7 has been conserved across lineages in both the subgenera Dr osophila and Sophophora.