Kuipers G K, Poldervaart H A, Slotman B J, Lafleur M V
Department of Radiotherapy, Section Radiobiology, Faculty of Medicine, Vrije Universiteit, van der Boechorststraat 7, Amsterdam, Netherlands.
Mutat Res. 1999 Oct 22;435(2):141-50. doi: 10.1016/s0921-8777(99)00043-9.
Base excision repair (BER) is a very important repair mechanism to cope with oxidative DNA damage. One of the most predominating oxidative DNA damages after exposure to ionizing radiation is 7, 8-dihydro-8-oxoguanine (8oxoG). This damage is repaired by formamidopyrimidine-DNA glycosylase (Fpg), a DNA glycosylase which is part of BER. Correct repair of 8oxoG is of great importance for cells, because 8oxoG has strong miscoding properties. Mispairing of 8oxoG with adenine instead of cytosine results in G:C to T:A transversion mutations. To determine the effect of a Fpg-deficiency on the spontaneous and gamma-radiation-induced mutation spectrum in the lacZ gene, double-stranded (ds) M13 DNA, with the lacZalpha gene inserted as mutational target, was irradiated with gamma-rays in aqueous solution under oxic conditions. Subsequently, the DNA was transfected into a wild-type Escherichia coli strain (JM105) and an isogenic Fpg-deficient E. coli strain (BH410). Although the overall spontaneous mutation spectra between JM105 and BH410 seemed similar, remarkable differences could be observed when the individual base pair substitutions were viewed. The amount of C to A transversions, which are most probably caused by unrepaired 8oxoG, has increased 3. 5-fold in the spontaneous BH410 spectrum. When the gamma-radiation-induced mutation spectra of JM105 and BH410 were compared, there was even a larger increase of C to A transversions in the BH410 strain (7-fold). We can therefore conclude that the straightforward approach used in this study confirms the importance of Fpg in repair of gamma-radiation-induced damage, and most probably especially in the repair of 8oxoG.
碱基切除修复（BER）是应对氧化性DNA损伤的一种非常重要的修复机制。暴露于电离辐射后最主要的氧化性DNA损伤之一是7,8 - 二氢 - 8 - 氧代鸟嘌呤（8 - 氧代鸟嘌呤，8oxoG）。这种损伤由甲酰胺嘧啶 - DNA糖基化酶（Fpg）修复，Fpg是一种属于碱基切除修复的DNA糖基化酶。正确修复8 - 氧代鸟嘌呤对细胞非常重要，因为8 - 氧代鸟嘌呤具有很强的错配特性。8 - 氧代鸟嘌呤与腺嘌呤而非胞嘧啶错配会导致G:C到T:A的颠换突变。为了确定Fpg缺陷对lacZ基因中自发和γ辐射诱导的突变谱的影响，将插入lacZα基因作为突变靶点的双链（ds）M13 DNA在有氧条件下于水溶液中用γ射线照射。随后，将DNA转染到野生型大肠杆菌菌株（JM105）和同基因的Fpg缺陷型大肠杆菌菌株（BH410）中。尽管JM105和BH410之间的总体自发突变谱看起来相似，但当观察单个碱基对替换时，可以观察到显著差异。最有可能由未修复的8 - 氧代鸟嘌呤引起的C到A的颠换数量，在BH410的自发突变谱中增加到了3.5倍。当比较JM105和BH410的γ辐射诱导突变谱时，BH410菌株中C到A的颠换增加得更多（7倍）。因此我们可以得出结论，本研究中使用的直接方法证实了Fpg在修复γ辐射诱导的损伤中的重要性，并且很可能尤其在修复8 - 氧代鸟嘌呤方面。
