Radiolabeled Cell Extracts Research Articles

A normal cell protein similar in structure and function to the avian sarcoma virus transforming gene product.

This report extends our previous studies concerning the identification and characterization of a protein from normal cells that is closely related to the avian sarcoma virus (ASV) transforming gene product pp60src. This normal cellular protein, which we have found in both avian and mammalian cells and have tentatively designated pp60sarc, was detected by immunoprecipitation of radiolabeled cell extracts with serum derived from both mice and rabbits bearing ASV-induced tumors. The normal cell pp60sarc is a 60,000-dalton phosphoprotein that is structurally similar, but not identical, to viral pp60src. The phosphorylation patterns of the normal cell and viral proteins are also similar: both contain two major phosphorylated residues, a phosphoserine located on the NH2-terminal 60% of the polypeptide and a phosphothreonine present on the COOH-terminal 40% of the molecule. In addition, the normal cell pp60sarc from both chicken and mammalian cells appears to have an associated protein kinase activity analogous to that previously described for the viral pp60src. The possible roles played by the normal cell protein pp60sarc and the ASV transforming protein pp60src in normal cellular growth and neoplastic disease, respectively, are discussed.

Partial characterization of cell-surface protein coded for by human chromosome 7

An antigen reactive with antisera to a human chromosome 7-coded cell-surface antigen can be extracted from human cells with the nonionic detergent NP-40. Immune complexes of radiolabeled cell extracts analyzed on SDS polyacrylamide gels showed a single protein with an apparent M.W. of approximately 165,000. This protein was immunoprecipitated from extracts of hybrid cells containing chromosome 7 and human cell extracts, but not from mouse cell extracts or from extracts of a hybrid clone without human chromosome 7. The data presented here indicate that the protein identified on the gels is a cell-surface glycoprotein coded for by human chromosome 7.

Identification of a transformation-specific antigen induced by an avian sarcoma virus

GENETIC analyses of avian sarcoma viruses (ASV) have led to the identification of a gene, designated src, which encodes a product required for the initiation and maintenance of neoplastic transformation in infected fibroblasts1–5. Because the src gene product has not been identified biochemically, this study was initiated to detect a transformation-specific protein, using serum from rabbits bearing ASV-induced tumours. We describe here the identification of a 60,000-MW transformation-specific antigen detectable in ASV-transformed chicken cells and ASV-induced hamster tumour cells by immunoprecipitation of radiolabelled cell extracts with serum from tumour-bearing rabbits. Moreover, the expression of this antigen is temperature dependent in chicken cells transformed by an ASV temperature-sensitive mutant in the src gene. The use of this antiserum may lead to the unequivocal identification and characterisation of the ASV src gene product and this, in turn, may lead to the elucidation of the mechanism of ASV-induced oncogenesis.