Ligation efficiency of one-nucleotide-gap and nicked DNA substrates by low-fidelity LIG1.A, lane 1 is the positive control for the ligation of pol β correct dGTP:C insertion product by WT LIG1. Lane 2 is the negative enzyme control of the one-nucleotide-gap DNA substrate with template base T. Lanes 3 to 6 and 7 to 10 show the self-ligation products by LIG1 WT and E346A/E592A (EE/AA) mutant, respectively, obtained at the time points 10, 30, 45, and 60 s. B, lane 1 is the negative enzyme control of the nicked DNA substrate with 3'-dA:T. Lanes 2 to 5 and 6 to 9 show the ligation products by LIG1 WT and E346A/E592A mutant, respectively, obtained at the time points 10, 30, 45, and 60 s. C, the graph shows the time-dependent changes in the ligation of the nicked DNA versus self-ligation of gap DNA products, and the data are presented as the averages from three independent experiments ± SDs. dGTP, guanine in the nucleotide pool; LIG1, DNA ligase I.