Fig. 1. Identification of Hox/Pbx- and Meis-binding sites within element C. Part of the chick element C sequence is shown, with the different binding sites (horizontal arrows) and the mutations that have been introduced into each of them (vertical arrows). Gel retardation analyses were performed with the probes schematized underneath the gels and the protein extracts indicated above. A cross within a site indicates that it is mutated. The retarded complexes are indicated by brackets and the specificity of the binding was established by competition with oligonucleotides carrying high-affinity Hox/Pbx- or Meis-binding sites (Competitor) or mutated versions unable to bind these factors (Mut competitor). FP, free probe.