Fig. 5. The eye-specific enhancer of ey contains a functional SO-binding site. (A) Genomic map of the ey locus between exon 2 (E2) and exon 3 (E3) (black boxes). The previously described eye-specific ey-enhancer is indicated by brackets. Relative positions of transposable elements that interfere with eye development are indicated by their allelic name (ey^R, ey²). The sequence of the eye-specific ey enhancer is given below (ey enhancer). B4M: the putative Pax6-binding sites (boxed) were mutated accordingly to Hauck et al. (Hauck et al., 1999) to get rid of toy-mediated signal. B4M SOmut: the putative Pax6-binding sites and additionally the putative SO-binding site (grey shaded) were mutated for comparison to B4M. (B) lacZ expression mediated by the wt ey-enhancer fragment in a third instar eye imaginal disc. (C) B4M-lacZ expression: without an influence of TOY protein, due to the mutated sites, the so-mediated expression is restricted to a portion of the posterior margin (similar to so9/Nr21 in Fig. 1C). (D) B4M SOmut-lacZ: mutating the Pax6 sites and the so site, expression is reduced to a weak spot in the centre of the posterior margin.