Figure 5. Redirecting a conserved enhancer.

In Drosophila melanogaster, 3′ enhancers (blue) activate ladybird expression (both the lbl and lbe genes) in the developing cardiac mesoderm. The lbe promoter contains paused Pol II, and has an enhancer blocking activity, preventing the activation of the neighboring C15 gene. In the flour beetle (Tribolium castaneum) the single ladybird gene is inverted relative to the orientation of the C15 locus. As a result the 3′ cardiac enhancer is able to activate C15 expression. Reproduced with permission from [118].