Sargentini N J, Smith K C
Department of Radiation Oncology, Stanford University School of Medicine, CA 94305-5105.
Mutat Res. 1992 Jan;265(1):83-101. doi: 10.1016/0027-5107(92)90041-y.
Experiments were designed to determine the association between the repair of gamma-radiation-induced DNA double-strand breaks (DSB) and the induction of 700-1000 bp long deletions (Lac(-)----Lac+), base substitutions (leuB19----Leu+), and frameshifts (trpE9777----Trp+) in Escherichia coli K-12. Over the range of 2.5-20 krad, deletions were induced with linear kinetics, as has been shown for the induction of DSB, while the induction kinetics of base substitutions and frameshifts were curvilinear. Like the repair of DSB, deletion induction showed an absolute requirement for an intact recB gene as well as a dependency on the type of preirradiation growth medium; these requirements were not seen for base substitutions or frameshifts. In addition, about 80% of the spontaneous deletions were absent in the recB21 strain. A recC1001 mutation, which confers a 'hyper-Rec' phenotype, increased the rate of gamma-radiation-induced deletions as well as the low-dose production of base substitutions and frameshifts. A recF143 mutation increased the yield of gamma-radiation-induced deletions without increasing base substitutions or frameshifts. A mutS mutation markedly enhanced the gamma-radiation induction of frameshifts, and had a slight effect on base substitutions, but did not affect the induction of deletions. Resistance to gamma-irradiation and the capacity to repair DSB (albeit at about half the normal rate) were restored to the radiosensitive recB21 strain by the addition of the sbcB21 and sbcC201 mutations. However, the radioresistant recB sbcBC strain, which is recombination proficient via the RecF pathway, was still grossly deficient in the ability to produce deletions. A model for deletion induction as a by-product of the recB-dependent (Chi-dependent) repair of gamma-radiation-induced DSB is discussed, as is the inability to detect deletions in cells that use only the recF-dependent (Chi-independent) mechanism to repair DSB.
设计实验以确定大肠杆菌K-12中γ射线诱导的DNA双链断裂（DSB）修复与700 - 1000碱基对长缺失（Lac(-)----Lac+）、碱基置换（leuB19----Leu+）和移码突变（trpE9777----Trp+）诱导之间的关联。在2.5 - 20千拉德范围内，缺失以线性动力学诱导，这与DSB诱导情况相同，而碱基置换和移码突变的诱导动力学呈曲线状。与DSB修复一样，缺失诱导对完整的recB基因有绝对需求，并且依赖于照射前生长培养基的类型；碱基置换或移码突变则不存在这些需求。此外，recB21菌株中约80%的自发缺失不存在。赋予“超Rec”表型的recC1001突变增加了γ射线诱导的缺失率以及低剂量下碱基置换和移码突变的产生。recF143突变增加了γ射线诱导的缺失产量，而不增加碱基置换或移码突变。mutS突变显著增强了γ射线诱导的移码突变，对碱基置换有轻微影响，但不影响缺失的诱导。通过添加sbcB21和sbcC201突变，对γ射线的抗性以及修复DSB的能力（尽管约为正常速率的一半）恢复到了辐射敏感的recB21菌株。然而，通过RecF途径具有重组能力的抗辐射recB sbcBC菌株在产生缺失的能力上仍然严重不足。讨论了将缺失诱导作为γ射线诱导的DSB的recB依赖性（依赖Chi）修复的副产物的模型，以及在仅使用recF依赖性（不依赖Chi）机制修复DSB的细胞中无法检测到缺失的情况。
