Figure 4.

Homeodomain binding sites are essential for enhancer activity and for binding of EdnrA-dependent factors. (A) Sequences of oligonucleotides S6–S9 and their mutant versions, containing several base changes, as indicated, destroying the ATTA motifs. (B) EMSA with wild-type and EdnrA^−/− first arch extract and oligonucleotides S7 and S7cla. Both the EdnrA-dependent complex (lane 1, black arrowhead), and the complex up-regulated in the absence of endothelin signaling (lane 2, white arrowhead; note distance to the ubiquitous complex indicated by the asterisk) are not formed on S7cla (lanes 3 and 4, respectively). (C) E10.5 F₀ embryo carrying construct 14, stained with Xgal. β-Galactosidase activity is observed in the heart (h), but not in the branchial arches (arrowheads).