Generation of specific H4IIEC3 nuclear protein–DNA complexes by the sequences from –81 to –61 of the rat carboxylase gene 5′-flanking region. Panel A shows cold competitor wild-type (WT) or mutant oligonucleotides with mutations made in groups of 3 adjacent bases (A, B, C, D) were added in the molar excesses indicated above each lane. Panel B shows cold competitor WT, B, or mutant oligonucleotides with mutations made in groups of 2 adjacent bases (E, F, G, H, I, J) were added in 100-fold molar excess, as indicated above each lane. Panel C shows cold competitor WT, B, or mutant oligonucleotides with mutations made outside the 12-bp core sequence, in groups of 2 adjacent bases (K, L, M, N), were added in 100-fold molar excess, as indicated above each lane. The arrow in all cases indicates the position of the upper complex referred to in “Results” and “Discussion.” Free indicates no added nuclear protein; (–), no added competitor.