Abstract
Escherichia coli DNA polymerase IV encoded by the dinB gene is involved in untargeted mutagenesis. Its human homologue is DNA polymerase [kappa] (Pol[kappa]) encoded by the DINB1 gene. Our recent studies have indicated that human Pol[kappa] is capable of both error-free and error-prone translesion DNA synthesis in vitro. However, it is not known whether human Pol[kappa] also plays a role in untargeted mutagenesis. To examine this possibility, we have measured the fidelity of human Pol[kappa] during DNA synthesis from undamaged templates. Using kinetic measurements of nucleotide incorporations and a fidelity assay with gapped M13mp2 DNA, we show that human Pol[kappa] synthesizes DNA with extraordinarily low fidelity. At the lacZ[alpha] target gene, human Pol[kappa] made on average one error for every 200 nucleotides synthesized, with a predominant T[Right arrow]G transversion mutation at a rate of 1/147. The overall error rate of human Pol[kappa] is 1.7-fold lower than human Pol[eta], but 33-fold higher than human Pol[beta], a DNA polymerase with very low fidelity. Thus, human Pol[kappa] is one of the most inaccurate DNA polymerases known. These results support a role for human Pol[kappa] in untargeted mutagenesis surrounding a DNA lesion and in DNA regions without damage.