Evolutionary dynamics of the enhancer region of even-skipped in Drosophila.
We report findings on naturally occurring variation in the regulatory region of even-skipped in Drosophila. This pair-rule gene encodes a homeobox-containing transcription factor, is expressed as a series of seven transverse stripes in developing embryos, and defines parasegmental boundaries. The 5' flanking region of the gene contains a 671-bp enhancer governing stripe 2 expression. The stripe 2 enhancer contains multiple binding sites for four transcription factors that provide positional information in developing blastoderm, the positive regulators bicoid and hunchback and the repressors giant and Kruppel. The study compares polymorphism and divergence in Drosophila melanogaster and Drosophila simulans for the enhancer region, the spacer between the enhancer and the transcription start site, the untranslated leader, the first exon and the intron of eve. Contrary to expectations, we find a relatively high level of variation in the stripe 2 enhancer region, including point substitutions and insertion/deletions in binding sites, and a comparable level of variation in the other noncoding regions. The patterns of variation and divergence within the enhancer region and between regions of the locus fit a model of neutral molecular evolution. We suggest that the multiplicity of binding sites in the enhancer provides a redundancy in function that allows flexibility in the sequence requirements and structural design of the promoter.
Department of Ecology and Evolution, University of Chicago, Illinois 60637, USA.
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Ludwig
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Kreitman
D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics; D004742:Enhancer Elements, Genetic; D019143:Evolution, Molecular; D005260:Female; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D014157:Transcription Factors / Q000378:metabolism
D001426:Bacterial Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; C052837:eve protein, Drosophila