The LP-BER was determined using an in vitro reconstituted assay system. Panel A shows the experimental protocol. The assay details are given in Materials and Methods. Panel B shows an autoradiogram of LP-BER, which is representative of three different experiments. Lane 1 shows 32P-labeled 63-mer F-DNA and Lane 2 shows the 23-mer product after APE1 incision. Lane 3 shows Pol-β-mediated strand-displacement synthesis. Lane 4 shows Pol-β-mediated strand-displacement synthesis stimulated by Fen1 (Lane 4). Lane 5 shows the complete repair of the 63-mer F-DNA through the LP-BER pathway in the presence of APE1, Pol-β, Fen1 and DNA ligase I. Lanes 6–9, 10–13, 14–17, 18–21 and 22–25 show the effect of different concentrations of the Pol-β inhibitors NSC 661073, 666713, 666715, 666717 and 666719 on LP-BER activity.