Fig. 3. A single Cubitus interruptus (Ci) binding site is crucial for activation of knot in the wing. (A) The locations of potential Ci-binding sites (seven out of nine residues or greater match consensus) are indicated in blue above the construct. Blocks of conserved sequence between D. melanogaster and D. pseudoobscura are indicated in red. A single nucleotide was altered individually in each of three conserved Ci-binding sites (indicated by a green or red `X'). Mutation of Ci1047 and Ci1341 sites has no effect (data not shown), whereas mutation of site Ci1680 (B) almost completely eliminates reporter gene expression.