Figure 7.
Accumulation of adenylylated DNA intermediate. A, abortive ligation mechanism observed under Mg2+-starved conditions. Adenylylated ligase interacts with nicked DNA substrates, generating adenylylated DNA intermediate. The partitioning between the nick-sealing steps and abortive ligation is represented with kseal and koff, respectively. Following successful or abortive ligation, ligase becomes adenylylated, preventing the enzyme from rebinding the adenylylated DNA intermediate and completing the nick-sealing step. B, propensity of DNA ligases for abortive ligation. Free Mg2+ concentrations were 70-fold below KMg for LIG1 and LIG3β in all experiments. The abortive ligation data represent multiple time points obtained from multiple-turnover time courses conducted in quadruplicate (see “Experimental procedures” for details). Error bars indicate S.D. from the mean.