Cellular mutation mediates T-antigen-positive revertant cells resistant to simian virus 40 transformation but not to retransformation by polyomavirus and adenovirus type 2

T-antigen-positive transformation revertant cell lines were isolated from fully simian virus 40 (SV40)-transformed Fisher rat embryo fibroblast cells (REF 52 cells) by methionine starvation. Reversion of the transformed cells (SV-52 cells) was caused by a mutation within the cellular genome. To demonstrate this, we isolated SV40 DNA from the host genome, inserted it into plasmid pSPT18 DNA, cloned it in Escherichia coli, and microinjected it into the nuclei of the REF 52 cells. Fully transformed cells were obtained with the same efficiency (20 to 25%) as after microinjection of wild-type SV40 DNA I. Furthermore, the revertant cells were resistant to retransformation by SV40. Following microinjection of wild-type SV40 DNA I, 42 independent cell lines were isolated. Cells of all analyzed lines acquired additional SV40 DNA copies, but changes in the cell morphology or growth characteristic were not demonstrable. However, the revertants were retransformable with a high efficiency after polyomavirus and adenovirus type 2 infections or microinjection. Also, fusion of the revertant cells with the grandparental REF 52 cells led to restoration of the transformed state.