Fig 1: Competition between SP-BER and LP-BER simultaneously in both upper and lower strands is compared with different combinations of repair enzymes. Competition between UDG and hOGG1 is shown in panels A and C, and between hTDG and hOGG1 in panels B and D. In panel A and B, SP-BER was completed by E. coli ligase, whereas in panels C and D, T4 ligase was used. In panel A, both strands were completely cleavage by UDG and hOGG1. Addition of pol ß and dGTP allowed complete repair of the lower strand (A, lane 5). Interestingly, simultaneous addition ofdGTP and dCTPresulted in less repair of the lower strand and significant amounts of truncated strands (A, lane 8). Replacement of UDG with hTDG allowed preferential repair of the lower strand. Similar results were obtained when E. coli ligase was replaced with T4 ligase (C&D).