Figure 3.

Transcription circuits can evolve in ways that preserve their output. The D. melanogaster sparkling enhancer (from the intergenic region of dPax2) and orthologous enhancers from related Drosophila species are shown at the left. There is very little primary sequence similarity among enhancers, as depicted by the different background colors. Binding sites for the transcription regulators Lozenge, Suppressor of Hairless, and Ets are depicted as magenta, cyan, and yellow boxes, respectively. As shown at the right, expression from this enhancer yields cone cell-specific expression in D. melanogaster. Despite the low overall DNA sequence similarity, cone cell-specific expression is maintained when orthologous sparkling enhancers are expressed in D. melanogaster.