The P-benzoquinone DNA Adducts Derived from Benzene Are Highly Mutagenic

Benzene is a human leukemia carcinogen, resulting from its cellular metabolism. A major benzene metabolite is p-benzoquinone (pBQ), which can damage DNA by forming the exocyclic base adducts pBQ-dC, pBQ-dA, and pBQ-dG in vitro. To gain insights into the role of pBQ in benzene genotoxicity, we examined in vitro translesion synthesis and in vivo mutagenesis of these pBQ adducts. Purified REV1 and Polkappa were essentially incapable of translesion synthesis in response to the pBQ adducts. Opposite pBQ-dA and pBQ-dC, purified human Poliota was capable of error-prone nucleotide insertion, but was unable to perform extension synthesis. Error-prone translesion synthesis was observed with Poleta. However, DNA synthesis largely stopped opposite the lesion. Consistent with in vitro results, replication of site-specifically damaged plasmids was strongly inhibited by pBQ adducts in yeast cells, which depended on both Polzeta and Poleta. In wild-type cells, the majority of translesion products were deletions at the site of damage, accounting for 91%, 90%, and 76% for pBQ-dA, pBQ-dG, and pBQ-dC, respectively. These results show that the pBQ-dC, pBQ-dA, and pBQ-dG adducts are strong blocking lesions, and are highly mutagenic by predominantly inducing deletion mutations. These results are consistent with the lesion structures predicted by molecular dynamics simulation. Our results led to the following model. Translesion synthesis normally occurs by directly copying the lesion site through base insertion and extension synthesis. When the lesion becomes incompatible in accommodating a base opposite the lesion in DNA, translesion synthesis occurs by a less efficient lesion loop-out mechanism, resulting in avoiding copying the damaged base and leading to deletion.