Mismatch repair and DNA polymerase ? proofreading prevent catastrophic accumulation of leading strand errors in cells expressing a cancer-associated DNA polymerase ? variant.

ABSTRACT: Substitutions in the exonuclease domain of DNA polymerase ? cause ultramutated human tumors. Yeast and mouse mimics of the most common variant, P286R, produce mutator effects far exceeding the effect of Pol? exonuclease deficiency. Yeast Pol?-P301R has increased DNA polymerase activity, which could underlie its high mutagenicity. We aimed to understand the impact of this increased activity on the strand-specific role of Pol? in DNA replication and the action of extrinsic correction systems that remove Pol? errors. Using mutagenesis reporters spanning a well-defined replicon, we show that both exonuclease-deficient Pol? (Pol?-exo-) and Pol?-P301R generate mutations in a strictly strand-specific manner, yet Pol?-P301R is at least ten times more mutagenic than Pol?-exo- at each location analyzed. Thus, the cancer variant remains a dedicated leading-strand polymerase with markedly low accuracy. We further show that P301R substitution is lethal in strains lacking Pol? proofreading or mismatch repair (MMR). Heterozygosity for pol2-P301R is compatible with either defect but causes strong synergistic increases in the mutation rate, indicating that Pol?-P301R errors are corrected by Pol? proofreading and MMR. These data reveal the unexpected ease with which polymerase exchange occurs in vivo, allowing Pol? exonuclease to prevent catastrophic accumulation of Pol?-P301R-generated errors on the leading strand.

SUBMITTER: Bulock CR 

PROVIDER: S-EPMC7498342 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature