Sedgwick B
Mol Gen Genet. 1983;191(3):466-72. doi: 10.1007/BF00425764.
The ada+ gene of E. coli is a regulatory gene of the adaptive response to simple alkylating agents. ada mutants are sensitive to both the mutagenicity and toxicity of alkylating agents, and are unable to induce O6-methylguanine DNA methyltransferase and 3-methyladenine DNA glycosylase II. The ada+ gene was cloned from wild type E. coli B by ligating bacterial DNA partially digested with Sau3A into the cosmid vector pJB8. The hybrid cosmid, pCS33, conveyed N-methyl-N'-nitro-N-nitrosoguanidine resistance to ada mutants of E. coli B and E. coli K12, and resulted in the constitutive synthesis of the two DNA repair enzymes at high levels. An alk mutation, which results in a deficiency of only the DNA glycosylase, was not complemented by this cosmid. It was concluded that the product of the ada+ gene is a positive regulator of the adaptive response. The cosmid insert DNA was subcloned into the plasmid vector pAT153, and the ada+ plasmids pCS42 and pCS58 selected. The ada+ gene was located in pCS58 by transposon mutagenesis and subcloning. Two polypeptides of Mr 37,000 and 27,000, were identified in 'maxi-cells' as products of the ada+ gene(s). It is as yet unclear whether they represent different forms of the same gene product, or are encoded by separate ada+ genes within the same operon.
大肠杆菌的ada+基因是对简单烷化剂适应性反应的一个调控基因。ada突变体对烷化剂的致突变性和毒性均敏感，且无法诱导O6-甲基鸟嘌呤DNA甲基转移酶和3-甲基腺嘌呤DNA糖基化酶II。通过将用Sau3A部分消化的细菌DNA连接到黏粒载体pJB8中，从野生型大肠杆菌B克隆出ada+基因。杂交黏粒pCS33赋予大肠杆菌B和大肠杆菌K12的ada突变体对N-甲基-N'-硝基-N-亚硝基胍的抗性，并导致两种DNA修复酶的组成型高水平合成。一个仅导致DNA糖基化酶缺陷的alk突变不能被这个黏粒互补。得出的结论是ada+基因的产物是适应性反应的一个正调控因子。将黏粒插入DNA亚克隆到质粒载体pAT153中，并筛选出ada+质粒pCS42和pCS58。通过转座子诱变和亚克隆将ada+基因定位在pCS58中。在“大细胞”中鉴定出两种分子量分别为37,000和27,000的多肽是ada+基因的产物。目前尚不清楚它们是代表同一基因产物的不同形式，还是由同一操纵子内不同的ada+基因编码。
