Ito T, Kobayashi K
Mutat Res. 1975 Oct;30(1):33-42. doi: 10.1016/0027-5107(75)90250-x.
The UV (270-nm) dose-frequency relationship for the induction of intragenic mitotic recombination at trp 5 locus in Saccharomyces cerevisiae was non-linear. Two parameters, alpha and a, in the proposed equation for the non-linear relationship f = (at)alpha were determined so as to fit the experimental data by the method of least squares. The analysis was extended over 5 cell stages during synchronous growth. It was found that (1) parameter alpha changed from 2.02 for unbudded small cells to 1.09 for the stage where the cell had finished the division of the nucleus, and (2) parameter a changed correspondingly from 7.25-10(-4) to 0.180-10(-4) sec-1 during the same period. One interesting outcome in this analysis was the deduction of a dose-dependent nature of relative sensitivity with respect to the stage. The determination of these two parameters enabled us to calculate dose-effect relationships beyond the limits of experimental restrictions. Such an "imaginary" relationship, calculated at an extremely low dose, revealed the existence of maximal sensitivity around the DNA synthesis period. It was further shown that this maximum would easily be masked even in the moderate dose range. Thus, we conclude that the validity of single dose comparisons is diminished unless alpha is constant regardless of the cell stage. Some considerations on the proposed parameters have been made in relation to the mechanisms of the induction of gene conversion by UV.
在酿酒酵母的trp 5位点诱导基因内有丝分裂重组时，紫外线（270纳米）剂量 - 频率关系是非线性的。通过最小二乘法确定了非线性关系f = (at)α的建议方程中的两个参数α和a，以拟合实验数据。分析扩展到同步生长的5个细胞阶段。结果发现：（1）参数α从未出芽小细胞的2.02变为细胞完成细胞核分裂阶段的1.09；（2）参数a在同一时期相应地从7.25×10⁻⁴变为0.180×10⁻⁴秒⁻¹。该分析的一个有趣结果是推断出相对敏感性对阶段的剂量依赖性。这两个参数的确定使我们能够计算超出实验限制范围的剂量 - 效应关系。在极低剂量下计算出的这种“虚拟”关系揭示了在DNA合成期左右存在最大敏感性。进一步表明，即使在中等剂量范围内，这种最大值也很容易被掩盖。因此，我们得出结论，除非α与细胞阶段无关是恒定的，否则单剂量比较的有效性会降低。已针对紫外线诱导基因转换的机制对所提出的参数进行了一些思考。
