In-Vitro Replication Studies on O2-Methylthymidine and O4-Methylthymidine

详细信息    查看全文

• 作者：Nisana Andersen ; Jianshuang Wang ; Pengcheng Wang ; Yong Jiang ; Yinsheng Wang
• 刊名：Chemical Research in Toxicology
• 出版年：2012
• 出版时间：November 19, 2012
• 年：2012
• 卷：25
• 期：11
• 页码：2523-2531
• 全文大小：371K
• 年卷期：v.25,no.11(November 19, 2012)
• ISSN：1520-5010

文摘

O²- and O⁴-methylthymidine (O²-MdT and O⁴-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 O²-MdT and O⁴-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^{鈥?/sup>), human DNA polymerase 魏 (pol 魏), and Saccharomyces cerevisiae DNA polymerase 畏 (pol 畏). Results from steady-state kinetic measurements and LC-MS/MS analysis of primer extension products revealed that Kf鈥?/sup> and pol 畏 preferentially incorporated the correct nucleotide (dAMP) opposite O2-MdT, while O4-MdT primarily directed dGMP misincorporation. While steady-state kinetic experiments showed that pol 魏-mediated nucleotide insertion opposite O2-MdT and O4-MdT is highly promiscuous, LC-MS/MS analysis of primer extension products demonstrated that pol 魏 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.}