Molecular analysis of duplicated esterase genes in Drosophila melanogaster

Genomic clones containing sequences homologous to an esterase 6 (Est-6) cDNA clone were isolated from a library of Drosophila melanogaster DNA. Comparison of the genomic and cDNA sequences revealed that the Est-6 gene comprises two exons, one of 1,387 bp and one of 248 bp, separated by a short intron of 51 bp. Further sequencing revealed the presence of a tandem duplication of the Est-6 gene (denoted Est-P) which also has an exon of 1,387 bp and an exon of 248 bp, separated by a short intron of 56 bp. The two genes show similarities of 64% and 60% at the DNA and protein levels, respectively. The coding regions of the genes are 197 bases apart, and presumptive 5' regulatory sequences of Est-P overlap at least the 3' noncoding region of Est-6. Transcripts homologous to Est-P were detected in late larvae and adults of each sex, whereas Est-6 transcripts are present in all life stages but are predominant in adult males. This suggests different physiological functions for the products of the two genes. Southern and Northern blot hybridization analyses of the 20-kb region surrounding the Est-6/Est-P duplication failed to detect any other duplicated esterase genes, although this region is actively transcribed.