In vitro Pol β synthesis with LP BER DNA intermediates. The Pol β synthesis reaction was carried out as described in Section 2 using (A) the 2-nucleotide gapped substrate, (B) the nicked CPD substrate, and (C) the nicked CPD-flap substrate for 0 (lane 1), 0.5 (lane 2), 1 (lane 3), and 1.5 (lane 4) min at 37°C. The positions of the primer band (14-mer for A and B; 16-mer for C) and extended product are shown.