A rapid kinetic experiment was used to measure the effects of increasing Mg2+ or Mn2+ concentrations on single nucleotide incorporation by DNA pol κ. The experiment was performed under enzyme limiting conditions (50 nM DNA pol κ, 100 nM template-primer DNA, and 0.5 mM dCTP) with MgCl2 (A) or MnCl2 (B) concentrations of 0.25 mM, 0.5 mM, 2 mM, 5 mM, and 8 mM. Burst amplitudes using MgCl2 were: A = 15 ± 4, 36 ± 4, 51 ± 4, 65 ± 5, and 62 ± 4 nM at each concentration respectively; and using MnCl2 were: A= 19 ± 4, 20 ± 1, 22 ± 2, 27 ± 2, and 43 ± 6 nM, respectively.