Partial characterization of a Moloney murine sarcoma virus 85,000-dalton polypeptide whose expression correlates with the transformed phenotype in cells infected with a temperature-sensitive mutant virus

Abstract

The viral proteins specified by a Moloney murine sarcoma virus (Mo-MuSV) with a temperature-sensitive mutation in its transforming gene were examined. Normal rat kidney cells infected with this replication-defective virus have transformed cell characteristics at 33° but revert to a normal phenotype at 40°. At the temperature permissive for transformation, the cells contained an 85,000-dalton protein (P85) which had antigenic determinants of p15, pp12, and p30, and also tryptic peptides characteristic of p15 and p30 as well as additional unidentified tryptic peptides. P85 was only detectable at the permissive temperature. A 58,000-dalton protein (P58) was also detected. It had both antigenic determinants and tryptic peptides of p15, pp12, and p30. P58 was seen at both temperatures. Phosphorylation experiments indicated that P58 is a phosphoprotein whereas 32P-labeled P85 was not observed. Temperature shift experiments showed that newly synthesized P85 was first detected between 2 and 3 hr following transfer of cultures to 33°. Morphological and biochemical changes indicative of transformation occurred 8 or more hr after temperature shift. These results are consistent with the interpretation that P85 contains peptide sequences derived from both the gag gene and the MuSV-acquired or src gene sequences.