Dorson J W, Moses R E
J Biol Chem. 1978 Feb 10;253(3):665-70.
DNA synthesis after ultraviolet irradiation is low in wild type toluene-treated cells. The level of repair incorporation is greater in strains deficient in DNA polymerase I. The low level of repair synthesis is attributable to the concerted action of DNA polymerase I and polynucleotide ligase. Repair synthesis is stimulated by blocking ligase activity with the addition of nicotinamide mononucleotide (NMN) or the use of a ligase temperature-sensitive mutant. NMN stimulation is specific for DNA polymerase I-mediated repair synthesis, as it is absent in isogenic strains deficient in the polymerase function or the 5' leads to 3' exonuclease function associated with DNA polymerase I. DNA synthesis that is stimulated by NMN is proportional to the ultraviolet exposure at low doses, nonconservative in nature, and is dependent on the uvrA gene product but is independent of the recA gene product. These criteria place this synthesis in the excision repair pathway. The NMN-stimulated repair synthesis requires ATP and is N-ethylmaleimide-resistant. The use of NMN provides a direct means for evaluating the involvement of DNA polymerase I in excision repair.
紫外线照射后，野生型甲苯处理细胞中的DNA合成水平较低。在缺乏DNA聚合酶I的菌株中，修复掺入水平更高。修复合成水平较低归因于DNA聚合酶I和多核苷酸连接酶的协同作用。通过添加烟酰胺单核苷酸（NMN）或使用连接酶温度敏感突变体来阻断连接酶活性，可刺激修复合成。NMN刺激对DNA聚合酶I介导的修复合成具有特异性，因为在缺乏聚合酶功能或与DNA聚合酶I相关的5'至3'外切核酸酶功能的同基因菌株中不存在这种刺激。由NMN刺激的DNA合成在低剂量下与紫外线暴露成正比，本质上是非保守的，并且依赖于uvrA基因产物，但不依赖于recA基因产物。这些标准将这种合成置于切除修复途径中。NMN刺激的修复合成需要ATP，并且对N-乙基马来酰亚胺具有抗性。使用NMN提供了一种直接手段来评估DNA聚合酶I在切除修复中的参与情况。
