Dynamic basis for dA•dGTP and dA•d8OGTP misincorporation via Hoogsteen base pairs

Replicative errors contribute to the genetic diversity needed for evolution but in high frequency can lead to genomic instability. Here, we show that DNA dynamics determine the frequency of misincorporating the A•G mismatch, and altered dynamics explain the high frequency of 8-oxoguanine (8OG) A•8OG misincorporation. NMR measurements revealed that A_anti•G_anti (population (pop.) of >91%) transiently forms sparsely populated and short-lived A_anti⁺•G_syn (pop. of ~2% and k_ex = k_forward + k_reverse of ~137 s^-1) and A_syn•G_anti (pop. of ~6% and k_ex of ~2,200 s^-1) Hoogsteen conformations. 8OG redistributed the ensemble, rendering A_anti•8OG_syn the dominant state. A kinetic model in which A_anti⁺•G_syn is misincorporated quantitatively predicted the dA•dGTP misincorporation kinetics by human polymerase β, the pH dependence of misincorporation and the impact of the 8OG lesion. Thus, 8OG increases replicative errors relative to G because oxidation of guanine redistributes the ensemble in favor of the mutagenic A_anti•8OG_syn Hoogsteen state, which exists transiently and in low abundance in the A•G mismatch.