LAUSR

Transformation of BALB/c-3T3 Cells by tsA Mutants of Simian Virus 40: Temperature Sensitivity of the Transformed Phenotype and Retransformation by Wild-Type Virus Brockman (W. W. Brockman, J Virol 25:860 – 870, 1978, http://jvi.asm.org/content/ 25/3/860.abstract) investigated the function of the A gene of simian virus 40 (SV40) in transformation of BALB/c-3T3 cells by infecting cells with wild-type (wt) SV40 and with six tsA mutants whose mutation sites map at different positions in the early region of the SV40 genome. Cells were infected at the permissive temperature, and cloned transformants were characterized for temperature sensitivity of the transformed phenotype. The majority of the tsA transformants, but none of the wt transformants, were temperature sensitive for maintenance of transformation. Furthermore, temperaturesensitive tsA transformants that were superinfected with wt SV40 were resistant to temperature inhibition of the transformed state. Since temperature-sensitive tsA transformants become temperature resistant on retransformation by wt virus, the temperature-sensitive defect lies in the product of a viral and not a cellular gene. These results imply that the protein encoded by the SV40 A gene is required to maintain the transformed phenotype in BALB/c-3T3 cells. The tsA gene encodes T antigen, and this study demonstrated that SV40 T antigen is required for transformation maintenance.