We report the mutational spectra in a segment of the E. coli rpoB gene of bleomycin (BLEO), 4-nitroquinoline-1-oxide (NQO), and hydrogen peroxide (H2O2). We compare these spectra with those of other mutagens and repair deficient strains in the same rpoB system, and review the key elements determining mutational hotspots and outline the questions that remain unanswered. We consider three tiers of hotspots that derive from 1) the nature of the sequence change at a specific base, 2) the direct nearest neighbors and 3) some aspect of the larger sequence context or the local 3D-structure of segments of DNA. This latter tier can have a profound effect on mutation frequencies, even among sites with identical nearest neighbor sequences. BLEO is dependent on the SOS-induced translesion Pol V for mutagenesis, and has a dramatic hotspot at a single mutational site in rpoB. NQO is not dependent on any of the translesion polymerases, in contrast to findings with plasmids treated in vitro and transformed into E. coli. The rpoB system allows one to monitor both G:C -> A:T transitions and G:C -> T:A transversions at the same site in 11 cases, each site having the identical sequence context for each of the two mutations. The combined preference for G:C -> A:T transitions at these sites is 20-fold. Several of the favored sites for hydrogen peroxide mutagenesis are not seen in the spectra of BLEO and NQO mutations, indicating that mutagenesis from reactive oxygen species is not a major cause of BLEO or NQO mutagenesis, but rather specific adducts. The variance in mutation rates at sites with identical nearest neighbors suggests that the local structure of different DNA segments is an important factor in mutational hotspots.

中文翻译：

---

大肠杆菌rpoB基因中由博来霉素，4-硝基喹啉-1-氧化物和过氧化氢诱导的突变：突变热点的观点。

我们报告了博来霉素（BLEO），4-硝基喹啉-1-氧化物（NQO）和过氧化氢（H2O2）的大肠杆菌rpoB基因片段的突变谱。我们将这些光谱与相同的rpoB系统中的其他诱变和修复缺陷菌株的光谱进行比较，并审查确定突变热点的关键要素，并概述仍未解决的问题。我们考虑了三层热点，这些热点来自：1）在特定碱基处的序列变化的性质，2）直接最近的邻居以及3）较大序列上下文的某些方面或DNA片段的局部3D结构。后者即使对具有相同最近邻序列的位点，也可以对突变频率产生深远影响。BLEO依赖于SOS诱导的转基因Pol V诱变，并且在rpoB的单个突变位点上具有惊人的热点。与在体外处理并转化到大肠杆菌中的质粒的发现相反，NQO不依赖于任何跨病变的聚合酶。rpoB系统允许在11种情况下，在同一位点同时监测G：C-> A：T转换和G：C-> T：A转换，每个位点对两种突变的序列上下文均相同。在这些站点上，G：C-> A：T过渡的组合偏好为20倍。在BLEO和NQO突变的光谱中未发现过氧化氢诱变的几个有利位点，这表明来自活性氧物种的诱变不是BLEO或NQO诱变的主要原因，而是特定的加合物。