Nucleotide polymorphism in the 5' promoter region of esterase 6 in Drosophila melanogaster and its relationship to enzyme activity variation.

Abstract

A 974-bp region immediately 5' of the esterase 6 gene was sequenced in 17 field derived third chromosome isoallelic lines. Twenty-three polymorphisms were identified, only two in the first 400 bp 5' but 16 in a 325-bp region from -494 to -819 bp. This distribution differs from previously published patterns in Drosophila simulans and D. mauritiana, where the first 800 bp are highly conserved. Fourteen common polymorphisms in the 325-bp region above are all in strong linkage disequilibrium with each other. Moreover, most of the haplotypes defined by the total of 23 polymorphisms fall into two groups that differ as a block at all 14 of these latter sites. Sequence differences between the two groups include some restriction sites that were scored in an earlier study of RFLPs and EST6 enzyme phenotypes among 42 isoallelic lines from the same population. By collating the two studies, we show that one haplotype group yields approximately 15% lower EST6 enzyme activity in adult males than the other. The promoter haplotypes show only weak disequilibrium with the esterase 6 fast/slow allozyme polymorphism, so it seems unlikely that previously reported latitudinal clines in the allozyme frequencies are due to their hitchhiking along with selection on the promoter difference.

The molecular evolution of development

“…Intraspecific variation in promoter sequences has been documented, and it is clear from molecular population genetic analysis that many promoters are constrained in their molecular evolution. (70,(76)(77)(78) The extent of this constraint is demonstrated in the promoter of the homeodomain pair-rule gene evenskipped (eve), which is expressed in Drosophila embryos in a series of stripes that define parasegmental boundaries. Population genetic analysis of five D. melanogaster and six D. simulans eve promoter alleles sampled over a broad geographic range estimate that this promoter is 2% diverged between the two species, although eve intron and silent coding sites display 6% divergence.…”

“…In the Esterase-6 promoter analyzed in 17 D. melanogaster lines, polymorphisms in a 325-bp region are found to be in strong linkage disequilibrium and are associated with a peak of variation approaching silent site levels. (77) This region contains elements that control Est-6 expression in the anterior sperm ejaculatory duct, and heterogeneity in this sequence may arise from yet undefined selective forces; two Est-6 promoter haplotype groups, designated P1 and P7, are associated with differences in male Est-6 activity in D. melanogaster.…”