The control of murine sarcoma virus (MSV) genetic information in rat cells transformed by a mutant was examined. Expression of the Cold-sensitive MSV transformed phenotype by cells after shift from the non permissive (33°) to the permissive temperature (39°) was not prevented by inhibitors of DNA and RNA synthesis but was prevented by inhibitors of protein and glycoprotein synthesis. Similar amounts of viral-specific RNA, measured by RNA-DNA hybridization, were found in cells grown at the permissive or nonpermissive temperature. The results suggest that the expression of transformation involves translational and possibly post-translational, but not transcriptional contro