Barfknecht T R, Shankel D M
Mutat Res. 1975 Nov;30(2):163-76.
When the excision proficient strain E. coli WP2 Hcr+ trp- was grown to stationary phase by glucose starvation in M-9 minimal medium before UV -irradiation, the ability of nutrient broth enrichment of minimal medium to enhance trp- leads to Trp+ reversion was greatly reduced. Less than 50% of the Trp+ revertants were found to be ochre suppressors. However, in the WWP2 Hcr- strain, 75-86% of the tested revertants were ochre suppressors. This indicates that, under the cultural conditions employed, many potential suppressor mutations were removed by excision repair in the presence of broth enrichment. Broth enhancement of reversion also occurred in the Hcr- strain, which indicates that a less error-prone mode of recombination repair functions under minimal growth conditions. An Hcr+ strr derivative of WP2 Hcr+ was more resistant than its strs parent to the lethal effect of UV light and showed a lower UV-induced Trp+ reversion frequency. The percentage of Trp+ revertants that were due to ochre suppressors was markedly reduced in the strr strain. The Hcr- strr strain also had a lower UV-induced Trp+ reversion frequency than its strs parent. The excision repair inhibitor caffeine had little effect at lower UV doses on increasing Trp+ reversion in both Hcr+ strains. Acriflavine, however, was effective at lower UV doses in enhancing reversiin of the Hcr+ strains and the degree of enhancement increased with the dose. Acriflavine appeared to specifically enhance the number of ochre suppressing Trp+ revertants. In both Hcr- strains (strs and strr) caffeine (500 mug/ml) had no effect on survival but reduced the UV-induced Trp+ reversion frequency acting as an antimutagen. In contrast, acriflavine (2 mug/ml) decreased survival and increased the Trp+ reversion frequency of the Hcr- strains. The data on spontaneous Trp+ reversion frequencies show that the Hcr+ strs strain had a higher spontaneous reversion frequency than the Hcr- strs strain on all plating media. Further, caffeine was shown to reduce spontaneous Trp+ reversion in both Hcr+ and Hcr- strains while acriflavine increased the spontaneous reversion frequencies of both strains.
当切除修复 proficient 菌株大肠杆菌 WP2 Hcr+ trp- 在 M-9 基本培养基中通过葡萄糖饥饿培养至稳定期后进行紫外线照射时，基本培养基中营养肉汤富集增强 trp- 导致 Trp+ 回复突变的能力大大降低。发现不到 50% 的 Trp+ 回复突变体是赭石抑制子。然而，在 WWP2 Hcr- 菌株中，75 - 86% 的测试回复突变体是赭石抑制子。这表明，在所采用的培养条件下，在肉汤富集存在的情况下，许多潜在的抑制子突变通过切除修复被去除。肉汤增强回复突变也发生在 Hcr- 菌株中，这表明在基本生长条件下，一种错误倾向较小的重组修复模式起作用。WP2 Hcr+ 的 Hcr+ strr 衍生物比其 strs 亲本对紫外线的致死效应更具抗性，并且显示出较低的紫外线诱导的 Trp+ 回复突变频率。在 strr 菌株中，由于赭石抑制子导致的 Trp+ 回复突变体的百分比显著降低。Hcr- strr 菌株的紫外线诱导的 Trp+ 回复突变频率也比其 strs 亲本低。切除修复抑制剂咖啡因在较低紫外线剂量下对增加两种 Hcr+ 菌株中的 Trp+ 回复突变几乎没有作用。然而，吖啶黄素在较低紫外线剂量下有效地增强了 Hcr+ 菌株的回复突变，并且增强程度随剂量增加。吖啶黄素似乎特异性地增加了赭石抑制 Trp+ 回复突变体的数量。在两种 Hcr- 菌株（strs 和 strr）中，咖啡因（500 μg/ml）对存活率没有影响，但作为抗诱变剂降低了紫外线诱导的 Trp+ 回复突变频率。相比之下，吖啶黄素（2 μg/ml）降低了 Hcr- 菌株的存活率并增加了 Trp+ 回复突变频率。关于自发 Trp+ 回复突变频率的数据表明，在所有平板培养基上，Hcr+ strs 菌株的自发回复突变频率高于 Hcr- strs 菌株。此外，咖啡因被证明可降低 Hcr+ 和 Hcr- 菌株中的自发 Trp+ 回复突变，而吖啶黄素增加了两种菌株的自发回复突变频率。
