Abbott P J
Mol Gen Genet. 1985;201(1):129-32. doi: 10.1007/BF00397998.
Previous studies have shown that transformation of Escherichia coli by plasmid DNA modified in vitro by carcinogens leads to RecA-dependant recombination between homologous plasmid and chromosomal DNA sequences. The mechanism of this recombination has now been studied using recombination-deficient mutants, and the influence of induction of the SOS response on the level of recombination investigated. Plasmid pNO1523, containing the str+ operon (Sms), has been modified in vitro by either irradiation with UV light, or by reaction with (+/-) trans-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) and used to transform streptomycin-resistant hosts. The formation of Ampr transformants which also carry streptomycin resistance was used as a measure of the level of recombination between plasmid and chromosomal DNA. Transformation of recB and recC mutants produced no change in the level of recombination while in the recF mutant a significant decrease was observed compared to the wild type host. Thermal induction of the SOS response in tif-1 and tif-1 umuC mutants followed by transformation led to a four-fold increase in recombination in both cases. The results suggest that the streptomycin-resistant transformants arise exclusively via a recombinational pathway which is largely dependant on the recF gene product, and that this pathway is influenced by induction of the SOS response. These results are discussed in terms of the mechanism of this recombination.
先前的研究表明，经致癌物体外修饰的质粒DNA转化大肠杆菌会导致同源质粒与染色体DNA序列之间发生RecA依赖性重组。现在已使用重组缺陷型突变体对这种重组的机制进行了研究，并研究了SOS应答的诱导对重组水平的影响。含有str+操纵子（Sms）的质粒pNO1523已通过紫外线照射或与（+/-）反式苯并（a）芘-7,8-二氢二醇-9,10-环氧化物（BPDE）反应在体外进行修饰，并用于转化抗链霉素宿主。同时携带链霉素抗性的Ampr转化体的形成被用作质粒与染色体DNA之间重组水平的一种衡量指标。recB和recC突变体的转化在重组水平上没有变化，而与野生型宿主相比，recF突变体中的重组水平显著降低。对tif-1和tif-1 umuC突变体进行SOS应答的热诱导，然后进行转化，在两种情况下重组都增加了四倍。结果表明，抗链霉素转化体完全通过主要依赖recF基因产物的重组途径产生，并且该途径受SOS应答诱导的影响。根据这种重组的机制对这些结果进行了讨论。
