Retransformation of ts SV40 Transformants by Murine Sarcoma Virus at Non-permissive Temperature

Abstract

Temperature sensitive (ts) SV40 transformed mouse fibroblasts (tsSV3T3) express their transformed phenotype in vitro when growing at 32° C but not when growing at 39° C¹. Viral mRNA is, however, apparently transcribed at 39° C, for SV40 specific T-antigen can be demonstrated and viral mRNA can be found by nucleic acid hybridization: Fusion-rescue experiments show that the transforming virus is wild type but tsSV3T3 cells cannot be re-transformed at 39° C with high multiplicity SV40. This suggests that the temperature sensitive behaviour stems from a cellular rather than a viral mutation. The question then arises of the stringency with which these ts transformants control the expression of viral transformation functions at 39° C.