Walker G C
J Bacteriol. 1978 Mar;133(3):1203-11. doi: 10.1128/jb.133.3.1203-1211.1978.
A screening procedure was developed for identifying mutants of the plasmid pKM101 no longer capable of enhancing mutagenesis. The test was based on the large pKM101-mediated increase in the number of Gal+ papillae observed on colonies of Salmonella typhimurium gal mutants plated on tetrazolium-galactose plates in the presence of a mutagen. The pKM101 mutant plasmids transferred normally, were stably maintained in cells, caused normal levels of ampicillin resistance, and still imparted sensitivity to phage Ike to their hosts. However, the pKM101 mutants had lost the ability to (i) enhance the reversion of both point and frameshift mutations, (ii) protect the cells against killing by UV irradiation, (iii) increase the spontaneous reversion rates of point mutations, (iv) enhance plasmid-mediated reactivation of UV-irradiated phage P22, (v) enhance Weigle reactivation. One pKM101 mutant with different properties from the others was identified by its increased spontaneous mutator effect. It is suggested that pKM101 amplifies the activity of the inducible error-prone repair systems in bacteria and that this is the function of pKM101 in the Ames Salmonella tester strains used for detection of carcinogens as mutagens.
已开发出一种筛选程序，用于鉴定不再能够增强诱变作用的质粒pKM101突变体。该测试基于在诱变剂存在下，在铺于四氮唑 - 半乳糖平板上的鼠伤寒沙门氏菌gal突变体菌落上观察到的由pKM101介导的Gal + 乳头数量的大幅增加。pKM101突变体质粒正常转移，在细胞中稳定维持，产生正常水平的氨苄青霉素抗性，并且仍然使其宿主对噬菌体Ike敏感。然而，pKM101突变体已失去以下能力：（i）增强点突变和移码突变的回复突变；（ii）保护细胞免受紫外线照射的杀伤；（iii）增加点突变的自发回复突变率；（iv）增强紫外线照射的噬菌体P22的质粒介导的再活化；（v）增强韦格勒再活化。通过其增加的自发诱变效应鉴定出一个与其他突变体具有不同特性的pKM101突变体。有人提出，pKM101可增强细菌中诱导性易错修复系统的活性，并且这是pKM101在用于检测作为诱变剂的致癌物的艾姆斯沙门氏菌测试菌株中的功能。
