DNA polymerase θ accomplishes translesion synthesis opposite 1,N6-ethenodeoxyadenosine with a remarkably high fidelity in human cells

: Here we show that translesion synthesis (TLS) opposite 1,N6-ethenodeoxyadenosine (edA), which disrupts Watson-Crick base pairing, occurs via Polι/Polζ-, Rev1-, and Polθ-dependent pathways. The requirement of Polι/Polζ is consistent with the ability of Polι to incorporate nucleotide opposite edA by Hoogsteen base pairing and of Polζ to extend synthesis. Rev1 polymerase and Polθ conduct TLS opposite edA via alternative error-prone pathways. Strikingly, in contrast to extremely error-prone TLS opposite edA by purified Polθ, it performs predominantly error-free TLS in human cells. Reconfiguration of the active site opposite edA would provide Polθ the proficiency for error-free TLS in human cells.