Mutation causing temperature-sensitive expression of cell transformation by a tumor virus (SV40-3T3 mouse...

A procedure has been devised to isolate 3T3 mouse fibroblasts transformed by simian virus 40 (SV40) that express their transformed phenotype at low (32 degrees C) but not at high (39 degrees C) temperature. Three parameters typical of malignant growth in vitro: (a) high saturation density in culture, (b) ability to form colonies on monolayers of normal 3T3 cells, and (c) lack of contact inhibition of DNA synthesis, are temperature sensitive. These phenotypic changes are fully reversible. The serum requirement for growth appears to be largely unchanged by temperature. These cells seem to owe their behavior to a cellular, rather than to a viral, alteration since after fusion of the temperature-sensitive transformed cells with permissive monkey cells, a procedure that leads to rescue (i.e., multiplication of the virus), wild-type SV40 virus is produced.