Fig. 3. Conservation of sequence, organization and activity of the E(spl)m PNC cis-regulatory module. (A) Alignment of orthologous genomic DNA segments corresponding to the E(spl)m PNC enhancer from D. melanogaster, D. pseudoobscura, D. hydei and D. virilis. Orthologous Su(H) (S) and proneural protein (E)-binding sites are connected by gray lines. (B) Nucleotide sequence alignments showing strong conservation (highlighted in green and yellow) in regions of the enhancer that contain Su(H) and proneural protein-binding sites (boxed). With the exception of S₄, the sequence of each binding site is precisely conserved, as is the spacing between S₂ and the E box. (C) The D. virilis E(spl)m module drives strong GFP expression (green) in PNCs of the late third-instar wing disc of D. melanogaster that is excluded from SOPs, similar to the D. melanogaster module (see Fig. 1B-D). Boxed region in 1 is shown at higher magnification on right (2-4); anti-Hnt staining (magenta) marks SOPs (1,3,4).