Mechanisms of accurate translesion synthesis by human DNA polymerase eta

The XPV (xeroderma pigmentosum variant) gene encodes human DNA polymerase e ta (pol eta), which is involved in the replication of damaged DNA, Pol eta catalyzes efficient and accurate translesion synthesis past cis-syn cyclobu tane di-thymine lesions. Here we show that human pol eta can catalyze trans lesion synthesis past an abasic (AP) site analog, N-2-acetylaminofluorene ( AAF)-modified guanine, and a cisplatin-induced intrastrand cross-link betwe en two guanines, Pol eta preferentially incorporated dAMP and dGMP opposite AP, and dCMP opposite AAF-G and cisplatin-GG, but other nucleotides were a lso incorporated opposite these lesions. However, after incorporating an in correct nucleotide opposite a lesion, pol eta could not continue chain elon gation. In contrast, after incorporating the correct nucleotide opposite a lesion, pol eta could continue chain elongation, whereas pol alpha could no t. Thus, the fidelity of translesion synthesis by human pol eta relies not only on the ability of this enzyme to incorporate the correct nucleotide op posite a lesion, but also on its ability to elongate only DNA chains that h ave a correctly incorporated nucleotide opposite a lesion.