Krisch R E
Int J Radiat Biol Relat Stud Phys Chem Med. 1976 Mar;29(3):249-54. doi: 10.1080/09553007614550281.
14C-2-thymidine was incorporated into the DNA of E. coli B/r and of coliphage T4. The labelled organisms were stored for several years at -196 degrees C. Both were periodically assayed for loss of viability, and the coliphage also for the appearance of double-strand breaks (DSBs) in DNA. E. coli B/r exhibited a survival curve with a substantial initial shoulder, extrapolation number 5-2 +/- 2-3, and a final exponential portion corresponding to a lethal efficiency per 14C decay per 2-5 X 10(9) daltons of DNA, of 0-009 +/- 0-002. For coliphage T4, our best estimate for the lethal efficiency per 14C decay is 0-03 +/- 0-04, and that for the DNA breakage efficiency is -0-002 +/- 0-004. The large standard errors result from the very small number of 14C decays occurring in each phage. These results suggest that 14C decay in the DNA of micro-organisms does not cause DSBs but does cause potentially lethal damage to the thymine bases in which decay occurs, and that wild-type E. coli can repair a large number of such DNA lesions.
14C - 2 - 胸苷被掺入大肠杆菌B/r和噬菌体T4的DNA中。标记后的生物体在-196℃下保存数年。定期检测两者的活力丧失情况，对噬菌体还检测DNA中双链断裂（DSB）的出现情况。大肠杆菌B/r呈现出一条具有明显初始肩部的存活曲线，外推数为5 - 2±2 - 3，以及最终的指数部分，对应于每2 - 5×10⁹道尔顿DNA每14C衰变的致死效率为0 - 009±0 - 002。对于噬菌体T4，我们对每14C衰变的致死效率的最佳估计为0 - 03±0 - 04，对DNA断裂效率的估计为 - 0 - 002±0 - 004。较大的标准误差是由于每个噬菌体中发生的14C衰变数量非常少。这些结果表明，微生物DNA中的14C衰变不会导致DSB，但会对发生衰变的胸腺嘧啶碱基造成潜在的致命损伤，并且野生型大肠杆菌能够修复大量此类DNA损伤。
