Vidal Leonardo S, Santos Larissa B, Lage Claudia, Leitão Alvaro C
Lab. Radiobiologia Molecular, Inst. Biofísica Carlos Chagas Filho, CCS-UFRJ, 21949540, Rio de Janeiro, RJ, Brazil.
Chem Res Toxicol. 2006 Oct;19(10):1351-6. doi: 10.1021/tx060035y.
Nucleotide excision repair (NER) in Escherichia coli repairs DNA by incising the damaged strand on the 3' and 5' sides of the lesion within pyrimidine dimers and DNA cross-linking adducts. Cross-linking adducts belong to a class of chemical damage to DNA that prevent strand separation, and thus, replication and transcription. For this reason, cross-linking agents such as mitomycin C (MC) have been used in cancer chemotherapy. The mechanisms involved in MC binding to DNA have already been defined; however, the repair of these lesions is not fully understood. Our goal was to study the repair of MC DNA lesions in E. coli cells. Several bacterial strains with specific mutations were tested for cellular inactivation and kinetics of DNA repair through analysis of DNA sedimentation profiles in alkaline sucrose gradients. The results obtained show that uvrB mutants are extremely sensitive to MC in contrast to the other isogenic uvrA and uvrC mutant strains. uvrB mutant strains are unable to repair DNA strand breaks produced by MC. Thus, UvrB might play a NER-uncoupled role in the repair of lesions induced by MC in vivo, different from its role on the repair of lesions produced by UV-C. Also it is suggested that a modified NER system is taking place in the repair of MC-adducts.
大肠杆菌中的核苷酸切除修复（NER）通过在嘧啶二聚体和DNA交联加合物的损伤位点的3'和5'侧切割受损链来修复DNA。交联加合物属于一类对DNA的化学损伤，可阻止链分离，从而阻止复制和转录。因此，诸如丝裂霉素C（MC）之类的交联剂已被用于癌症化疗。MC与DNA结合所涉及的机制已经明确；然而，这些损伤的修复尚未完全了解。我们的目标是研究大肠杆菌细胞中MC诱导的DNA损伤的修复。通过分析碱性蔗糖梯度中的DNA沉降图谱，对几种具有特定突变的细菌菌株进行细胞失活和DNA修复动力学测试。所得结果表明，与其他同基因uvrA和uvrC突变菌株相比，uvrB突变体对MC极为敏感。uvrB突变菌株无法修复由MC产生的DNA链断裂。因此，UvrB可能在体内修复MC诱导的损伤中发挥NER非偶联作用，这与其在修复UV-C产生的损伤中的作用不同。此外，有人提出在MC加合物的修复中发生了一种改良的NER系统。
