Processing of thymine glycol in a clustered DNA damage site: mutagenic or cytotoxic
Processing of thymine glycol in a clustered DNA damage site: mutagenic or cytotoxic
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DOI：
10.1093/nar/gkp422
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发表时间：
2009-07-01
影响因子：
14.9
通讯作者：
O'Neill, Peter
中科院分区：
文献类型：
--
作者：
Bellon, Sophie;Shikazono, Naoya;O'Neill, Peter
损伤的局部聚集是某些DNA损伤剂的标志，特别是电离辐射。由含有AP位点、8-氧代-7，8-二氢鸟嘌呤（8-oxoG）或5，6-二氢胸腺嘧啶的组合的簇状损伤位点的影响引起的遗传变化的可能性很高。到目前为止，还没有研究过含有DNA碱基损伤的簇，所述DNA碱基损伤是复制聚合酶的强阻断剂。由于胸腺嘧啶二醇（Tg）是非致突变性的，但复制聚合酶的一个强大的块，我们已经调查了是否含有Tg的集群是高度致突变性或导致潜在的细胞毒性病变时，密切反对8-oxoG或AP网站。使用基于细菌质粒的测定和使用细胞提取物或纯化蛋白质的修复测定，我们已经表明，当Tg与AP位点相反时，DNA双链断裂（DSB）出现，无论是通过尝试碱基切除修复还是在复制时。相比之下，在簇中与Tg相对的8-oxoG“保护”免于DSB形成，但相对于在单个8-oxoG处的突变频率确实增强了在8-oxoG位点处的突变频率，这是由于内切核酸酶在加工Tg/8-oxoG簇的初始阶段中的决定性作用，去除Tg以得到具有脱碱基位点或单链断裂的中间体。
Localized clustering of damage is a hallmark of certain DNA-damaging agents, particularly ionizing radiation. The potential for genetic change arising from the effects of clustered damage sites containing combinations of AP sites, 8-oxo-7,8-dihydroguanine (8-oxoG) or 5,6-dihydrothymine is high. To date clusters containing a DNA base lesion that is a strong block to replicative polymerases, have not been explored. Since thymine glycol (Tg) is non-mutagenic but a strong block to replicative polymerases, we have investigated whether clusters containing Tg are highly mutagenic or lead to potentially cytotoxic lesions, when closely opposed to either 8-oxoG or an AP site. Using a bacterial plasmid-based assay and repair assays using cell extracts or purified proteins, we have shown that DNA double-strand breaks (DSBs) arise when Tg is opposite to an AP site, either through attempted base excision repair or at replication. In contrast, 8-oxoG opposite to Tg in a cluster 'protects' against DSB formation but does enhance the mutation frequency at the site of 8-oxoG relative to that at a single 8-oxoG, due to the decisive role of endonucleases in the initial stages of processing Tg/8-oxoG clusters, removing Tg to give an intermediate with an abasic site or single-strand break.