Transformation of BALB/c-3T3 cells by tsA mutants of simian virus 40: temperature sensitivity of the transformed phenotype and retransofrmation by wild-type virus
Transformation of BALB/c-3T3 cells by tsA mutants of simian virus 40: temperature sensitivity of the transformed phenotype and retransofrmation by wild-type virus
复制标题
猿猴病毒40的tsA突变体转化BALB/c-3T3细胞：转化表型的温度敏感性和野生型病毒的再转化
作者：
W. W. Brockman
用野生型SV40和6个突变位点位于SV40基因组早期不同位置的TSA突变体，在允许的温度下感染猴病毒40(SV40)的A基因，研究其在转化BALB/c-3T3细胞中的作用。然后对克隆的转化子进行了表型的温度敏感性鉴定。在16个TSA转化子中，15个对正常细胞的单层生长能力是温度敏感的，而3个野生型转化子中有3个不是。当选择的无性系在软琼脂和含低浓度血清的培养基中生长时，也观察到了转化表型的这种温度敏感性模式。一个例外的TSA转化子的耐温性既不是由于突变位点在转化病毒中的位置，也不是因为突变病毒的转化。然而，这个耐高温的TSA转化子比由同一TSA突变体转化的温度敏感系含有更高的SV40T抗原浓度。在不允许的温度下表现未转化表型的TSA转化子对野生型病毒在该温度下的再转化很敏感，这表明TSA转化子的温度敏感性是由于病毒突变而不是细胞缺陷。这些结果表明，在BALB/c-3T3细胞中保持转化表型需要SV40A基因产物的持续表达。
The function of the A gene of simian virus 40 (SV40) in transformation of BALB/c-3T3 cells was investigated by infecting at the permissive temperature with wild-type SV40 and with six tsA mutants whose mutation sites map at different positions in the early region of the SV40 genome. Cloned transformants were then characterized as to the temperature sensitivity of the transformed phenotype. Of 16 tsA transformants, 15 were temperature sensitive for the ability to overgrow a monolayer of normal cells, whereas three of three wild-type transformants were not. This pattern of temperature sensitivity of the transformed phenotype was also observed when selected clones were assessed for the ability to grow in soft agar and in medium containing low concentration of serum. The temperature resistance of the one exceptional tsA transformant could be attributed neither to the location of the mutation site in the transforming virus nor to transformation by a revertant virus. This temperature-resistant tsA transformant, however, was demonstrated to contain a higher intracellular concentration of SV40 T antigen than a temperature-sensitive line transformed by the same tsA mutant. A tsA transformant displaying the untransformed phenotype at the nonpermissive temperature was found to be susceptible to retransformation by wild-type virus at this temperature, demonstrating that the temperature sensitivity of the tsA transformants is due to the viral mutation and not to a cellular defect. These results indicate that continuous expression of the product of the SV40 A gene is required to maintain the transformed phenotype in BALB/c-3T3 cells.