Panel A, gel shift assays were carried out as in Figure 5B, using the indicated antibodies (Aby) to immunologically probe the protein-DNA complexes identified. Panel B, the α-Smad2/3 antibody that recognizes Smad2(FL), Smad2Δexon3, and Smad3 specifically inhibits formation of complexes 2–4 (lanes 1–2). However, antibodies specific for Smad3 (lanes 4–5) or Smad4 (7–8) did not have any effect. See Supplement Figures S1 and S2 for validation of Smad3 and Smad4 antibodies.