Syntheses and characterizations of the in vivo replicative bypass and mutagenic properties of the minor-groove O2-alkylthymidine lesions
作者:Qianqian Zhai、Pengcheng Wang、Qian Cai、Yinsheng Wang
DOI:10.1093/nar/gku748
日期:2014.9.15
Endogenous metabolism, environmental exposure, and treatment with some chemotherapeutic agents can all give rise to DNA alkylation, which can occur on the phosphate backbone as well as the ring nitrogen or exocyclic nitrogen and oxygen atoms of nucleobases. Previous studies showed that the minor-groove O2-alkylated thymidine (O2-alkyldT) lesions are poorly repaired and persist in mammalian tissues. In the present study, we synthesized oligodeoxyribonucleotides harboring seven O2-alkyldT lesions, with the alkyl group being a Me, Et, nPr, iPr, nBu, iBu or sBu, at a defined site and examined the impact of these lesions on DNA replication in Escherichia coli cells. Our results demonstrated that the replication bypass efficiencies of the O2-alkyldT lesions decreased with the chain length of the alkyl group, and these lesions directed promiscuous nucleotide misincorporation in E. coli cells. We also found that deficiency in Pol V, but not Pol II or Pol IV, led to a marked drop in bypass efficiencies for most O2-alkyldT lesions. We further showed that both Pol IV and Pol V were essential for the misincorporation of dCMP opposite these minor-groove DNA lesions, whereas only Pol V was indispensable for the T→A transversion introduced by these lesions. Depletion of Pol II, however, did not lead to any detectable alterations in mutation frequencies for any of the O2-alkyldT lesions. Thus, our study provided important new knowledge about the cytotoxic and mutagenic properties of the O2-alkyldT lesions and revealed the roles of the SOS-induced DNA polymerases in bypassing these lesions in E. coli cells.
内源代谢、环境暴露和某些化疗药物的治疗都会导致 DNA 烷基化,这种烷基化可能发生在核碱基的磷酸骨架、环氮或外环氮原子和氧原子上。以前的研究表明,小凹槽 O2-烷基化胸苷(O2-alkyldT)病变修复能力差,并在哺乳动物组织中持续存在。在本研究中,我们合成了含有 7 个 O2-alkyldT(烷基为 Me、Et、nPr、iPr、nBu、iBu 或 sBu)病变的寡脱氧核苷酸,并考察了这些病变对大肠杆菌细胞中 DNA 复制的影响。我们的研究结果表明,O2-烷基ldT病变的复制旁路效率随着烷基链长的增加而降低,这些病变在大肠杆菌细胞中引导了杂乱的核苷酸错结合。我们还发现,缺乏 Pol V(而不是 Pol II 或 Pol IV)会导致大多数 O2-alkyldT 病变的旁路效率明显下降。我们进一步发现,Pol IV 和 Pol V 对于与这些小凹槽 DNA 病变相对的 dCMP 错结合都是必不可少的,而只有 Pol V 对于这些病变引入的 T→A 转换是不可或缺的。然而,Pol II 的耗竭并没有导致任何 O2-alkyldT病变的突变频率发生任何可检测到的变化。因此,我们的研究为 O2-alkyldT 病变的细胞毒性和突变特性提供了重要的新知识,并揭示了 SOS 诱导的 DNA 聚合酶在大肠杆菌细胞中绕过这些病变的作用。