Sidorkina O, Saparbaev M, Laval J
Groupe Réparation des Lésions Radio- et Chimio-Induites, URA 147 CNRS. Institut Gustave Roussy, Villejuif, France.
Mutagenesis. 1997 Jan;12(1):23-8. doi: 10.1093/mutage/12.1.23.
Deoxyinosine occurs in DNA by spontaneous deamination of adenine or by incorporation of dITP during replication. Hypoxanthine residues (HX) are mutagenic and give rise to A-T-->G-C transition. They are substrates for the Escherichia coli product of the alkA gene, the 3-methyl-adenine-DNA glycosylase II (ALK A protein). In mammalian cells and in yeast, HX is excised by the counterpart of ALK A protein, the ANPG or the MAG proteins respectively. We have investigated in vivo the contribution of the alkA gene to counteract the lethal and/or mutagenic effects of HX residues induced by nitrous acid treatment. Using an E.coli strain allowing the detection of A-T-->G-C transition, we show that the alkA mutant has a slightly increased spontaneous rate of mutation and about the same sensitivity when treated with HNO2 as compared with the wild-type strain. Using the E.coli alkA mutant carrying a multicopy plasmid expressing the ALK A protein or the ANPG protein, we barely observe any effect of HNO2 treatment on sensitivity and mutation rate of the bacteria. In contrast, the same experiment performed with a uvrA- strain, deficient in nucleotide excision repair (NER), shows that this mutant is extremely sensitive to HNO2 treatment. Furthermore, the sensitivity and the spontaneous mutation rate observed in the double mutant alkA- uvrA- are almost identical to those of the uvrA- mutant. Hence, NER has the major role in vivo for the repair of lethal and mutagenic lesions induced by HNO2.
脱氧肌苷在DNA中通过腺嘌呤的自发脱氨作用或在复制过程中dITP的掺入而出现。次黄嘌呤残基(HX)具有致突变性,会导致A-T→G-C转换。它们是大肠杆菌alkA基因产物3-甲基腺嘌呤-DNA糖基化酶II(ALK A蛋白)的底物。在哺乳动物细胞和酵母中,HX分别由ALK A蛋白的对应物ANPG或MAG蛋白切除。我们在体内研究了alkA基因在对抗亚硝酸处理诱导的HX残基的致死和/或致突变作用方面的贡献。使用一种能够检测A-T→G-C转换的大肠杆菌菌株,我们发现与野生型菌株相比,alkA突变体的自发突变率略有增加,在用HNO2处理时敏感性大致相同。使用携带表达ALK A蛋白或ANPG蛋白的多拷贝质粒的大肠杆菌alkA突变体,我们几乎没有观察到HNO2处理对细菌敏感性和突变率的任何影响。相比之下,用缺乏核苷酸切除修复(NER)的uvrA-菌株进行的相同实验表明,该突变体对HNO2处理极其敏感。此外,在双突变体alkA-uvrA-中观察到的敏感性和自发突变率与uvrA-突变体几乎相同。因此,在体内,NER在修复由HNO2诱导的致死和致突变损伤方面起主要作用。