Roufa D J, Sadow B N, Caskey C T
Genetics. 1973 Nov;75(3):515-30. doi: 10.1093/genetics/75.3.515.
In order to obtain a large collection of Chinese hamster cell clones defective in thymidine kinase (TK(-)), BrdU(r) selection experiments have been performed on wild-type and revertant TK(+) cell lines. No clones (< 10(-9)) were obtained from the wild-type TK(+) cell line by single-step selection. In contrast, revertant TK(+) clones readily gave rise to stable TK(-) derivatives (1 - 2 x 10(-4)). Both wild-type and revertant TK(+) clones spontaneously yielded 8-AG(r) colonies with the same frequency (1 - 5 x 10(-6)), suggesting that the differences between wild-type and revertant cell lines specifically affected selection of the TK(-) phenotype. The increased frequency of TK(-) clones reflects perhaps the number (ploidy) or character of the autosomal TK loci in TK(+) revertants, or perhaps the mechanisms which regulate expression of the TK genes. Several mutagens, EMS, MNNG and UV, stimulated the TK(+) revertants' frequency of TK(-) subclones only slightly (< 3-fold). Biochemical and genetic data indicated that the TK(-) clones derived from one revertant are phenotypically different. The phenotypes displayed by these cell lines are stable and do not depend upon the continued presence of the selective agent.
为了获得大量胸苷激酶缺陷型（TK(-)）的中国仓鼠细胞克隆，已对野生型和回复突变型TK(+)细胞系进行了BrdU(r)选择实验。通过单步选择，未从野生型TK(+)细胞系中获得克隆（<10(-9)）。相比之下，回复突变型TK(+)克隆很容易产生稳定的TK(-)衍生物（1 - 2×10(-4)）。野生型和回复突变型TK(+)克隆自发产生8-AG(r)菌落的频率相同（1 - 5×10(-6)），这表明野生型和回复突变型细胞系之间的差异特异性地影响了TK(-)表型的选择。TK(-)克隆频率的增加可能反映了TK(+)回复突变体中常染色体TK基因座的数量（倍性）或特征，或者可能反映了调节TK基因表达的机制。几种诱变剂，即EMS、MNNG和紫外线，仅略微刺激了TK(+)回复突变体中TK(-)亚克隆的频率（<3倍）。生化和遗传数据表明，源自一个回复突变体的TK(-)克隆在表型上是不同的。这些细胞系所显示的表型是稳定的，不依赖于选择剂的持续存在。
