Billen D, Hewitt R R, Lapthisophon T, Achey P M
J Bacteriol. 1967 Nov;94(5):1538-45. doi: 10.1128/jb.94.5.1538-1545.1967.
A comparison of repair synthesis after ultraviolet light (UV) or X-ray exposure was made in Escherichia coli strains 15T(-) (555-7) and B/r by use of a D, (15)N, (13)C density labeling system. During the initial 15 min of incubation after UV irradiation, both a "repair" synthesis and a reduced semiconservative deoxyribonucleic acid (DNA) synthesis occurred. In the so-called "physiological" dose range used, the latter was greater than the former. X-irradiation of cells, at doses producing similar levels of cell death as in the UV-exposed cultures, did not lead to a similar repair replication process. However, a density heterogeneity of the DNA synthesized in the initial 10 min after exposure was observed. This is interpreted in terms of X ray-induced DNA degradation. Normal cells showed only a semiconservative type of replication and, therefore, within the limits of resolution of the system used (the incorporation of 1,000 to 5,000 nucleotides per replicating chromosome could be measured), DNA in normal cells did not appear to undergo a repair synthesis involving thymine exchange. These results indicate that not all repair mechanisms mimic that found after UV exposure.
利用D、（15）N、（13）C密度标记系统，对大肠杆菌15T（-）（555 - 7）和B/r菌株在紫外线（UV）或X射线照射后的修复合成进行了比较。在紫外线照射后的最初15分钟孵育期间，既发生了“修复”合成，也出现了减少的半保留脱氧核糖核酸（DNA）合成。在所使用的所谓“生理”剂量范围内，后者大于前者。对细胞进行X射线照射，剂量产生的细胞死亡水平与紫外线照射培养物中的相似，但并未导致类似的修复复制过程。然而，在照射后的最初10分钟内观察到合成的DNA存在密度异质性。这被解释为X射线诱导的DNA降解。正常细胞仅表现出半保留类型的复制，因此，在所使用系统的分辨率范围内（可测量每个复制染色体掺入1000至5000个核苷酸），正常细胞中的DNA似乎未经历涉及胸腺嘧啶交换的修复合成。这些结果表明，并非所有的修复机制都与紫外线照射后发现的机制相似。
