Binding of nuclear proteins is specific. EMSA of nuclear extract derived from HepG2 cells bound to the −401T fragment in the presence of unlabeled DNA as competitor. Arrows 1 and 2 refer to the allele-specific factors. Lane 1, without extract; lane 2, 0.20 mg/mL of HepG2 extract in the absence of competitor; lanes 3 to 6, 0.20 mg/mL of HepG2 extract in the presence of 200-fold excess of unlabeled DNA as competitor. Competitors used were: −402A site (lane 3), WT site (lane 4), −401T site (lane 5), and nonrelated 30 bp fragment (lane 6).