After incorporating two dAMPs opposite the thymine-thymine cyclobutane pyrimidine dimer (TT-CPD), DNA polymerase eta (POLH) can continue translesion DNA synthesis (TLS). POLH preferentially incorporates dAMPs and dGMPs, and may introduce one error per every 18-380 nucleotides (dNMPs) added. POLH stalls after incorporation of a mispaired dNMP, which limits POLH- mediated mutagenesis, in addition to the subsequent polymerase switch (Matsuda et al. 2000, Masutani et al. 2000).