Touati E, Krin E, Quillardet P, Hofnung M
Unité de Programmation Moléculaire & de Toxicologie Génétique/CNRS Ura 1444, Institut Pasteur, Paris, France.
Carcinogenesis. 1996 Dec;17(12):2543-50. doi: 10.1093/carcin/17.12.2543.
The mutagenic specificity of 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), a very potent genotoxic 2-nitrofuran, was investigated in the lacI gene of E.coli. To analyze the influence of SOS-mutagenesis on R7000-induced mutations, 86 and 84 LacI- mutants were respectively isolated from umuC+ and umuC strains. Treatment of bacteria with increasing concentrations of R7000, affected 2-4 times more the survival rate in the umuC context, as compared to umuC+. 80% of all mutations occurred primarily at G:C base pairs and were substitution events and single-base frameshifts (-1) in the same proportions. The six possible substitution events were observed in both strains. In the umuC+ context, they were dominated by G:C-->T:A transversions. 38% of substitutions at G:C base pairs occurred in the consensus sequence 5'TGGCG3' or 5'TGGC3' where the G was mutated. When umuC was deficient G:C-->C:G transversions were mainly observed. The proportions of substitution mutations were very similar to those that have been reported for apurinic (AP) sites, suggesting strongly that one mechanism for R7000-induced mutations is the formation of intermediate abasic sites that serve as a substrate for error-prone repair. Single frameshift events consisted essentially of deletions of one (G:C) base pair in runs of contiguous G or C residues. Frameshift frequency increased with the length of the reiterated sequence, suggesting a strand-slippage process. Other mutational classes were recovered to a lower extent, including double-base frameshifts and large deletions. In addition, 10% of the mutants presented two proximate mutations. Comparison of the mutations induced by R7000 in the umuC+/umuC backgrounds suggests an influence of the umuC product on strand specificity of R7000-induced mutations, particularly in the case of frameshift events.
对一种极具遗传毒性的2-硝基呋喃——7-甲氧基-2-硝基萘并[2,1-b]呋喃（R7000）的诱变特异性，在大肠杆菌的lacI基因中进行了研究。为分析SOS诱变对R7000诱导突变的影响，分别从umuC⁺和umuC菌株中分离出86个和84个LacI⁻突变体。用浓度递增的R7000处理细菌，与umuC⁺相比，在umuC背景下对存活率的影响要高出2至4倍。所有突变的80%主要发生在G:C碱基对，且为替换事件和单碱基移码突变（-1），二者比例相同。在两种菌株中均观察到六种可能的替换事件。在umuC⁺背景下，它们以G:C→T:A颠换为主。G:C碱基对处38%的替换发生在共有序列5'TGGCG3'或5'TGGC3'中，其中G发生了突变。当umuC缺陷时，主要观察到G:C→C:G颠换。替换突变的比例与报道的无嘌呤（AP）位点的比例非常相似，强烈表明R7000诱导突变的一种机制是形成中间无碱基位点，作为易错修复的底物。单移码事件基本上由连续的G或C残基序列中一个（G:C）碱基对的缺失组成。移码频率随重复序列长度增加而增加，表明存在链滑动过程。其他突变类型的发生率较低，包括双碱基移码和大片段缺失。此外，10%的突变体出现了两个相邻突变。R7000在umuC⁺/umuC背景下诱导的突变比较表明，umuC产物对R7000诱导突变的链特异性有影响，尤其是在移码事件的情况下。
