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

Abstract Replicative errors contribute to the genetic diversity needed for evolution but in high frequency can lead to genomic instability. The mechanisms determining the frequency of DNA copying errors are not fully understood. Here, we show DNA dynamics determines the frequency of misincorporating the A-G mismatch and altered dynamics explains the high frequency of 8-oxoguanine (8OG) A-8OG misincorporation. NMR measurements revealed Aanti-Ganti (pop. >91%) transiently forms sparsely-populated and short-lived Aanti+-Gsyn (pop. ~ 2% and kex=kforward + kreverse ~ 137 s− 1) and Asyn-Ganti (pop. ~ 6% and kex ~ 2200 s− 1) Hoogsteen conformations. 8OG redistributed the ensemble rendering Aanti-8OGsyn the dominant state. A kinetic model in which Aanti+-Gsyn is misincorporated quantitatively predicted the kinetics of dA-dGTP misincorporation by human polymerase b, the pH dependence of misincorporation, and the impact of the 8OG lesion. Thus, 8OG increases replicative errors by increasing the abundance of a pre-existing, sparsely-populated, short-lived, and mutagenic Aanti+-Gsyn Hoogsteen state.