Temperature-dependent expression of transformation by cold-sensitive mutant of murine sarcoma virus

Morphological transformation of normal rat kidney cells by a murine sarcoma virus was found to be cold-sensitive. Cells transformed by the virus expressed their transformed phenotype at the permissive temperature (39 degrees ) but not at the nonpermissive temperature (33 degrees ), as judged by the criteria of morphological changes and colony-forming ability on monolayers of normal rat kidney cells. Cold-sensitive expression of transformation was specific for focus-derived normal rat kidney cells transformed by the virus, readily reversible, and not lost during serial propagation of the cells. The genome of the murine sarcoma virus can be rescued by superinfection with Moloney leukemia virus at the permissive or nonpermissive temperature, and the rescued virus exhibited the same cold-sensitive properties as the original transforming virus. These results suggest that maintenance of the transformed state is continuously dependent on a cold-sensitive viral function.