ABSTRACT
When human DNA polymerase eta (pol eta) encounters N6-deoxyadenosine adducts formed by trans epoxide ring opening of the 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE) isomer with (+)-7R,8S,9S,10R configuration ((+)-BaP DE-2), misincorporation of A or G and incorporation of the correct T are equally likely to occur. On the other hand, the enzyme exhibits a 3-fold preference for correct T incorporation opposite adducts formed by trans ring opening of the (-)-(7S,8R,9R,10S)-DE-2 enantiomer. Adducts at dA formed by cis ring opening of these two BaP DE-2 isomers exhibit a 2-3-fold preference for A over T incorporation, with G intermediate between the two. Extension one nucleotide beyond these adducts is generally weaker than incorporation across from them, but among mismatches the (adducted A*) x A mispair is the most favored for extension. Because mutations can only occur if mispairs are extended, this observation is consistent with the occurrence of A x T to T x A transversions as common mutations in animal cells treated with BaP DE-2 isomers. Adducts with S absolute configuration at the point of attachment of the hydrocarbon to the base inhibit incorporation and extension by pol eta to a lesser extent than their R counterparts. Template-primers containing each of the four isomeric dA adducts derived from BaP DE-2 and two adducts derived from 9,10-epoxy-7,8,9,10-tetrahydrobenzo-[a]pyrene in which the 7- and 8-hydroxyl groups of the DEs are replaced with hydrogens exhibit reduced electrophoretic mobilities relative to the unadducted oligonucleotides. This effect is largely independent of DNA sequence. Decreased mobility correlates with an increased rate of incorporation by pol eta, suggesting a systematic relationship between the overall DNA structure and efficiency of the enzyme.
