title: In-vitro replication studies on O(2)-methylthymidine and O(4)-methylthymidine.
abstract: O(2)- and O(4)-methylthymidine (O(2)-MdT and O(4)-MdT) can be induced in tissues of laboratory animals exposed with N-methyl-N-nitrosourea, a known carcinogen. These two O-methylated DNA adducts have been shown to be poorly repaired and may contribute to the mutations arising from exposure to DNA methylating agents. Here, in vitro replication studies with duplex DNA substrates containing site-specifically incorporated O(2)-MdT and O(4)-MdT showed that both lesions blocked DNA synthesis mediated by three different DNA polymerases, including the exonuclease-free Klenow fragment of Escherichia coli DNA polymerase I (Kf(-)), human DNA polymerase κ (pol κ), and Saccharomyces cerevisiae DNA polymerase η (pol η). Results from steady-state kinetic measurements and LC-MS/MS analysis of primer extension products revealed that Kf(-) and pol η preferentially incorporated the correct nucleotide (dAMP) opposite O(2)-MdT, while O(4)-MdT primarily directed dGMP misincorporation. While steady-state kinetic experiments showed that pol κ-mediated nucleotide insertion opposite O(2)-MdT and O(4)-MdT is highly promiscuous, LC-MS/MS analysis of primer extension products demonstrated that pol κ favorably incorporated the incorrect dGMP opposite both lesions. Our results underscored the limitation of the steady-state kinetic assay in determining how DNA lesions compromise DNA replication in vitro. In addition, the results from our study revealed that, if left unrepaired, O-methylated thymidine lesions may constitute important sources of nucleobase substitutions emanating from exposure to alkylating agents.
authors.affiliation: Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
authors.forename: Nisana
authors.initials: N
authors.lastname: Andersen
authors.forename: Jianshuang
authors.initials: J
authors.lastname: Wang
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Jiang
authors.forename: Yinsheng
authors.initials: Y
authors.lastname: Wang
mesh_terms: D004247:DNA / Q000096:biosynthesis / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D019384:Nucleic Acid Synthesis Inhibitors; D010100:Oxygen / Q000737:chemistry / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013936:Thymidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D019384:Nucleic Acid Synthesis Inhibitors; D004247:DNA; C012439:methylthymidine; D004259:DNA-Directed DNA Polymerase; D010100:Oxygen; D013936:Thymidine