Fig. 2. The localization of binding sites within CR1. (A) Sequences of probes used in EMSA experiments to localize the binding of factors within CR1. The region of interest described in Fig. 1B,C is marked by black arrows. Mutations; m1, m2, m3 and m4 are underlined and the sequences important for binding are boxed. (B) Results of EMSA experiments using probes depicted in A: E, 10.5dpc mouse embryo whole-cell extract; F9 EC, F9 EC nuclear extract; Neuro2a, Neuro2a whole-cell extract. Black arrows indicate the position of the two retarded bands. (C,D) EMSA experiments comparing HoxTF/YY1 sites from different genes, by competition (C) and direct binding (D). HoxPwt contains wild-type (wt) sequences from +143 to +169 of the Hoxb4 5'-untranslated region and myogenin comprises sequences from +9 to + 35 of the mouse myogenin promoter (Yee and Rigby, 1993; Gutman et al., 1994). MyoD contains sequences from –628 to –602 of the mouse MyoD1 gene (Zingg et al., 1991). Myogenin-mut and MyoDm contain the mutation CCA to AAC at positions +17 to +19 and –620 to –618, respectively.