Figure 4.

C1 binds specifically to the a2 promoter in at least three locations. A, A radiolabeled fragment of the a2 promoter, spanning −161 to +5, was mixed with purified C1 protein in the presence or absence of competitor oligonucleotides or C1 and non-C1 antibodies. The specific competitor is a C1-binding site from the a1 promoter (−76 to −47). The mutant competitor is the same fragment of a1, but with 2-bp substitutions that reduce activation (Grotewold et al., 1994) and C1 DNA binding (Sainz et al., 1997). B through D, Methylation interference experiments using purified C1 Myb protein and the indicated end-labeled oligonucleotides of the a2 promoter (see Methods). Lanes U contain methylation-interference reactions purified from unbound labeled probe. Lanes B contain reactions purified from bound probe. The sequence to the left of each gel corresponds to the sequence of the oligonucleotide, with the protected region boxed.