Specht S M, Sideropoulos A S
Department of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania 15282.
Microbios. 1990;62(252-253):187-95.
The number of UV-induced mutations to streptomycin resistance in Escherichia coli B/r cells depends on the post-irradiation incubation medium. When cells are incubated on phosphate buffer agar (PBA) as opposed to brain heart infusion agar (BHI), there is an irreversible loss in the number of potential streptomycin resistant mutants which develop. This decrease in mutant numbers is known to occur without a corresponding loss in overall cell viability and cannot be explained in terms of the kinetics of dimer excision. Recent studies have indicated that pyrimidine dimers are the substrate for this repair on PBA. The genetics of PBA repair was investigated by observing the influence of the post-irradiation incubation medium (PBA vs BHI) on the number of streptomycin resistant mutants which develop in E. coli strains deficient in various repair pathways. A recB and recC strain (WP3 recB trp-; WP7 recC trp-) showed repair of potential streptomycin resistant mutants similar to that of B/r when incubated on PBA following irradiation. The medium had no effect on the number of mutants expressed in an excision deficient uvrA- strain (WP2 uvrA trp-) or a polymerase I mutant (P3478 polA thy-). This was interpreted to mean that the loss of streptomycin resistant mutants on PBA involves the excision repair pathway and is dependent on the polA gene product, polymerase I.
大肠杆菌B/r细胞中紫外线诱导的对链霉素抗性的突变数量取决于照射后的培养介质。与脑心浸液琼脂（BHI）相比，当细胞在磷酸盐缓冲琼脂（PBA）上培养时，产生的潜在链霉素抗性突变体数量会出现不可逆的减少。已知这种突变体数量的减少在总体细胞活力没有相应损失的情况下发生，并且无法用二聚体切除动力学来解释。最近的研究表明，嘧啶二聚体是PBA上这种修复的底物。通过观察照射后的培养介质（PBA与BHI）对缺乏各种修复途径的大肠杆菌菌株中产生的链霉素抗性突变体数量的影响，研究了PBA修复的遗传学。recB和recC菌株（WP3 recB trp-；WP7 recC trp-）在照射后在PBA上培养时，显示出与B/r类似的潜在链霉素抗性突变体的修复。该培养基对切除缺陷的uvrA-菌株（WP2 uvrA trp-）或聚合酶I突变体（P3478 polA thy-）中表达的突变体数量没有影响。这被解释为意味着PBA上链霉素抗性突变体的减少涉及切除修复途径，并且依赖于polA基因产物聚合酶I。
