Krisch R E, Krasin F, Sauri C J
Int J Radiat Biol Relat Stud Phys Chem Med. 1976 Jan;29(1):37-50. doi: 10.1080/09553007614551541.
Iodine-125 decays by electron capture and is known to cause extensive molecular fragmentation via the Augur effect. 125I was incorporated into the DNA of exponentially-growing E. coli K12 AB2487, a recA mutant, and E. coli K12 AB2497, the corresponding rec+ strain, as 5-iododeoxyuridine (IUdR), an analogue of thymidine. Radioactive bacteria were stored at - 196 degrees C, and samples were periodically assayed for loss of viability and for the induction of double-strand breaks (DSBs) in DNA. Each 125I decay in the DNA of either strain induces one DSB, i.e. alpha(DSB) = 1.0. For the recA strain, alpha(lethal) = 0.9 and for the rec+ strain, 0.4. Assays for biological repair of DSBs, involving incubation of thawed samples in growth-medium at 37 degrees C before the extraction of DNA, demonstrate significant repair of 125I-induced DSBs by rec+ cells but none by recA cells. For small numbers of decays, there is approximately a 1:1 correlation, for either strain, between lethal decays and post-incubation residual DSBs. Comparison with data for larger numbers of decays indicates that a typical rec+ cell can repair no more than three to four DSBs per completed genome (2.5 x 10(9) daltons).
碘 - 125通过电子俘获衰变，已知会通过俄歇效应导致广泛的分子碎片化。125I以胸苷类似物5 - 碘脱氧尿苷（IUdR）的形式掺入指数生长的大肠杆菌K12 AB2487（一种recA突变体）和大肠杆菌K12 AB2497（相应的rec +菌株）的DNA中。放射性细菌保存在 - 196℃，定期检测样本的活力丧失以及DNA中双链断裂（DSB）的诱导情况。任一菌株DNA中的每次125I衰变都会诱导一次DSB，即α(DSB) = 1.0。对于recA菌株，α(致死) = 0.9，对于rec +菌株，α(致死) = 0.4。对DSB生物修复的检测包括在提取DNA之前将解冻的样本在37℃的生长培养基中孵育，结果表明rec +细胞能显著修复125I诱导的DSB，而recA细胞则不能。对于少量衰变，任一菌株的致死衰变与孵育后残留的DSB之间大约存在1:1的相关性。与大量衰变数据的比较表明，一个典型的rec +细胞每个完整基因组（2.5×10^9道尔顿）修复的DSB不超过三到四个。
