A Dominant Role for an Error‐Prone DNA Polymerase in Recombination Drives Evolution

Abstract

Homologous recombination (HR) repairs double‐strand breaks in DNA by directing replication to copy sequence information from a homologous donor DNA. Importantly, this mode of repair is considered error‐free which implies that only high‐fidelity DNA polymerases (pols) perform recombination‐directed replication (RDR). Yet in E. coli, error‐prone Y‐family translesion pols function with RecA recombinase, are highly upregulated in response to stress, and promote mutations following DSBs, which suggests a possible role for these mutagenic pols in HR. Here, we investigate E. coli translesion pol activity in HR by reconstituting RDR in vitro. We find that translesion pol IV is proficient in RDR even without the β‐processivity clamp, whereas translesion pol V lacks this activity. Notably, low‐fidelity pol IV initiates RDR more efficiently than high‐fidelity replicative pol III and is preferentially recruited to D‐loop recombination intermediates under stress response conditions. Unexpectedly, we find that pol III is inhibited in RDR due to its proofreading activity which is stimulated at D‐loops. Finally, we show that pol IV promotes mutations during RDR. These data demonstrate a dominant role for error‐prone pol IV in HR and elucidate the molecular basis of adaptive mutagenesis which facilitates evolution under conditions of stress.