Efficiency of radiation-induced base lesion excision and the order of enzymatic treatment
Efficiency of radiation-induced base lesion excision and the order of enzymatic treatment
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DOI：
10.1080/09553002.2017.1239849
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发表时间：
2017-03
影响因子：
2.6
通讯作者：
Iyo Shiraishi;N. Shikazono;Masao Suzuki;K. Fujii;A. Yokoya
中科院分区：
文献类型：
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作者：
Iyo Shiraishi;N. Shikazono;Masao Suzuki;K. Fujii;A. Yokoya
摘要目的：阐明在包含多个碱基损伤的成簇DNA损伤位点处的初始碱基切除修复过程是否通过糖基化酶和脱嘌呤/脱嘧啶（AP）核酸内切酶碱基切除酶形成额外的链断裂而影响后续切除过程。材料与方法：以质粒DNA（pUC 18）为模型DNA分子，在不同条件下，用高线性能量转移（LET）电离辐射（He ~（2+）或C ~（6+）离子）或低LET电离辐射（X射线）照射，产生不同的自由基清除效应。然后用两种细菌碱基切除酶（糖基化酶），即内切核酸酶III和甲酰氨基嘧啶-DNA糖基化酶依次或同时处理pUC 18，它们分别将嘧啶（或脱碱基[AP]位点）和嘌呤（或AP位点）损伤转化为单链断裂（SSB）。在改变酶处理的顺序后，检查作为消化产物的额外SSB或双链断裂（DSB）的产率。结果如下：酶处理之间几乎没有差异，表明处理顺序不影响由糖基化酶活性形成的额外SSB或DSB的最终产率。这表明，在总损伤中，具有持续性基底损伤的簇状损伤部位的分数取决于糖基化酶处理的顺序，如果存在的话是不显著的。结论：由高或低LET辐射诱导的碱基病变簇出现三个或更多个碱基对分开，并迅速转化为DSB的糖基化酶，无论酶处理的顺序。
Abstract Purpose: To clarify whether initial base excision repair processes at clustered DNA damage sites comprising multiple base lesions affect subsequent excision processes via the formation of additional strand breaks by glycosylase and apurinic/apyrimidinic (AP) endonuclease base excision enzymes. Materials and methods: Plasmid DNA (pUC18) as a model DNA molecule was exposed to high-linear-energy-transfer (LET) ionizing radiation (He2+ or C6+ ions) or low-LET ionizing radiation (X-rays) under various conditions to produce varied radical-scavenging effects. pUC18 was then treated sequentially or simultaneously with two bacterial base excision enzymes (glycosylases), namely, endonuclease III and formamidopyrimidine-DNA glycosylase, which convert pyrimidine (or abasic [AP] site) and purine (or AP site) lesions to single-strand breaks (SSB), respectively. Yields of additional SSB or double-strand breaks (DSB) as digestion products were examined after changing the order of enzymatic treatment. Results: There were few differences among the enzymatic treatments, indicating that treatment order did not affect the final yields of additional SSB or DSB formed by glycosylase activity. This suggests that of the total damage, the fraction of clustered damage sites with a persistent base lesion dependent on the order of glycosylase treatment was insignificant if present. Conclusion: Base lesion clusters induced by high- or low-LET radiation appear three or more base pairs apart, and are promptly converted to a DSB by glycosylase, regardless of the order of enzymatic treatment.