Detection of the Viral Sarcoma Gene Product in Cells Infected with Various Strains of Avian Sarcoma Virus and of a Related Protein in Uninfected Chicken Cells

ABSTRACT

Genetic analyses have defined a single gene (src) as that portion of the avian sarcoma virus (ASV) genome which encodes the protein directly responsible for ASV-induced neoplastic transformation. We have recently identified the polypeptide product of the src gene of the Schmidt-Ruppin (SR) strain of ASV, a 60,000-dalton phosphoprotein designated pp60^src, and have further determined that pp60^src acts as a protein kinase. Essential to the identification and characterization of the pp60^src protein of SR-ASV was the use of serum (TBR serum) from rabbits bearing SR-ASV-induced tumors. TBR serum was, however, strain specific, recognizing pp60^src from SR-ASV-transformed cells only. We report here that sera from marmosets bearing tumors induced by the Bryan or SR strains of ASV (TBM sera) contain antibody which precipitates the transforming gene product from cells transformed by the SR, Bryan, Prague, or Bratislava strains of ASV. In contrast, rabbits bearing tumors induced by either the Bratislava or Bryan strains of ASV, or hamsters with SR-ASV-induced tumors did not produce antibody to pp60^src from any strain of ASV. The 60,000-dalton polypeptides immunoprecipitated with TBM serum from cells transformed by each of the above virus strains are phosphoproteins. One-dimensional peptide mapping by limited proteolysis revealed that the pp60^src proteins are structurally very similar, but not identical. Furthermore, all of the viral pp60^src proteins have an associated phosphotransferase activity. In addition to detecting the viral src proteins, TBM serum was able to immunoprecipitate an antigenically related protein from normal uninfected avian cells.