Identification of a polypeptide enc( sarcoma virus src gene (cell-free protein synthesis/translation of viral RNA/immunopre4

Two' techniques were used to search for the polypeptide encoded by the avian sarcoma virus (ASV) sre gene. First, antiserum from rabbits bearing ASV-induced fibrosar- comas was used to immunoprecipitate a transformation-specific antigen from ASV-transformed chick embryo fibroblasts. This antigen has an apparent molecular weight (Mr) of 60,000. Sec- ond, the 3' one-third of the ASV'genome, selected by oligo(dT)- cellulose chromatography and sucrose gradient sedimentation, was translated in a mRNA-dependent reticulocyte cell-free lysate. This RNA species programmed the synthesis of a poly- peptide that comigrated with the transformation-specific an- tigen of Mr 60,000 immunoprecipitated from transformed cells. The methionine-containing tryptic peptides from the polypep- tides of Mr 60,000 obtained from translation in vitro and from immunoprecipitation were found to be identical upon two- dimensional fractionation.