TEMPO AND MODE OF EVEN-SKIPPED STRIPE-2 ENHANCER EVOLUTION IN DROSOPHILA

Regulatory sequences controlling important developmental genes are wid ely viewed as being functionally and evolutionarily constrained by tem poral and cell-specific demands on expression. However, the evolution of gene regulation is also viewed as being an important factor in morp hogenetic change. To address this issue, we compare sequences of the e ven-skipped (eve) stripe 2 enhancer and promoter region within and bet ween species of Drosophila. The analysis reveals a large number of nuc leotide substitutions in regulatory protein binding sites (bicoid, hun chback, kruppel and giant), as well as a systematic change in the size of the enhancer. We argue that natural selection must be playing a po sitive role in the evolution of the stripe 2 enhancer.