Keller P, Zownir O, Morrow J
Mutat Res. 1984 Mar;126(1):53-62. doi: 10.1016/0027-5107(84)90169-6.
We have studied multiple step bromodeoxyuridine (BrdU) resistance in Friend leukemia cells. The mutation rate to 30 micrograms/ml resistance was 5.1 X 10(-5) per cell per generation, and to 100 micrograms/ml was 3.7 X 10(-7) per cell per generation. Resistant variants could not be obtained in a single step using BrdU concentrations higher than 100 micrograms/ml. Three clones isolated through multiple step selection were resistant to 640 micrograms/ml of BrdU and deficient in thymidine kinase, although their ability to transport radiolabeled thymidine was unimpaired relative to wild type. All three clones had low reversion frequencies, as judged by plating efficiencies in couterselective HAT medium. Two such revertant clones were isolated and tested for their forward mutation frequency in BrdU. No resistant clones were obtained when as many as 5 X 10(7) cells were tested. This observation argues against the hypothesis that the Friend cells possess two functional thymidine kinase loci and that the revertants represent a heterozygous condition. We conclude that the hypothesis of null mutations within a hemizygous or heterozygous thymidine kinase locus is sufficient to account for high-level BrdU resistance in Friend leukemia cells.
我们研究了弗氏白血病细胞对多步溴脱氧尿苷（BrdU）的抗性。对30微克/毫升抗性的突变率为每细胞每代5.1×10⁻⁵，对100微克/毫升的突变率为每细胞每代3.7×10⁻⁷。使用高于100微克/毫升的BrdU浓度无法在一步中获得抗性变体。通过多步选择分离出的三个克隆对640微克/毫升的BrdU具有抗性且胸苷激酶缺陷，尽管它们转运放射性标记胸苷的能力相对于野生型未受损。根据在反选择HAT培养基中的平板效率判断，所有三个克隆的回复频率都很低。分离出两个这样的回复克隆并测试它们在BrdU中的正向突变频率。当测试多达5×10⁷个细胞时，未获得抗性克隆。这一观察结果反对弗氏细胞拥有两个功能性胸苷激酶基因座且回复体代表杂合状态的假设。我们得出结论，半合子或杂合子胸苷激酶基因座内的无效突变假说是足以解释弗氏白血病细胞中高水平BrdU抗性的。
