Watanabe M, Suzuki N, Sawada S, Nikaido O
Carcinogenesis. 1984 Oct;5(10):1293-9. doi: 10.1093/carcin/5.10.1293.
We compared the frequencies of mutation and morphological transformation in relation to the repair of potentially lethal damage (PLD) and sublethal damage (SLD) in X-irradiated golden hamster embryo (GHE) cells. The repair of PLD induced in GHE cells by X-rays was shown to be an error-free process which reduced the frequency of mutation and morphological transformation. However, if cells were irradiated with doses divided into two halves separated by various time intervals to study repair of SLD, the frequency of mutants and morphological transformants depended upon the length of the interval between the doses. If the interval was 2 h, the frequency of mutants and transformants was lower than if the total dose were delivered in a single exposure. If the interval was 4 h, these frequencies were higher than the latter. The transformation frequencies remained high even if this interval was increased to 12 h, but the frequency of mutants decreased again. Thus, enhancement of mutant or transformant frequency by a second exposure to X-rays, 4 h after the first irradiation, correlated with recovery of DNA synthesis in the X-irradiated cell populations. Studies with synchronized cells also showed that induction of mutants and transformants was highest in cells irradiated at the DNA synthesis (S) phase. These results suggest that DNA synthesis plays a critical role in the process of X-ray-induced morphological transformation and mutagenesis.
我们比较了X射线照射的金黄仓鼠胚胎（GHE）细胞中，与潜在致死性损伤（PLD）和亚致死性损伤（SLD）修复相关的突变频率和形态转化频率。结果表明，X射线诱导的GHE细胞中PLD的修复是一个无差错过程，该过程降低了突变频率和形态转化频率。然而，如果用不同时间间隔分成两半的剂量照射细胞以研究SLD的修复，突变体和形态转化体的频率则取决于两次剂量之间的间隔时间长度。如果间隔为2小时，突变体和转化体的频率低于单次照射给予总剂量时的频率。如果间隔为4小时，这些频率则高于后者。即使该间隔增加到12小时，转化频率仍然很高，但突变体频率再次下降。因此，在第一次照射后4小时再次暴露于X射线导致突变体或转化体频率增加，这与X射线照射的细胞群体中DNA合成的恢复相关。对同步化细胞的研究还表明，在DNA合成（S）期照射的细胞中，突变体和转化体的诱导率最高。这些结果表明，DNA合成在X射线诱导的形态转化和诱变过程中起着关键作用。
