NORMAL-CELL PROTEIN SIMILAR IN STRUCTURE AND FUNCTION TO THE AVIAN-SARCOMA VIRUS TRANSFORMING GENE-PRODUCT

This report extends our previous studies concerning the indentification and characterization of a protein from normal cells that is closely related to the avian sarcoma virus (ASV) transforming gene product pp60(src). This normal cellular protein, which we have found in both avian and mammalian cells and have tentatively designated pp60(sarc), was detected by immunoprecipitation of radiolabeled cell extracts with serum derived from both mice and rabbits bearing ASV-induced tumors. The normal cell pp60(sarc) is a 60,000-dalton phosphoprotein that is structurally similar, but not identical, to viral pp60(src). The phosphorylation patterns of the normal cell and viral proteins are also similar: both contain two major phosphorylated residues, a phosphoserine located on the NH 2-terminal 60% of the polypeptide and a phosphothreonine present on the COOH-terminal 40% of the molecule. In addition, the normal cell pp60(sarc) from both chicken and mammalian cells appears to have an associated protein kinase activity analogous to that previously described for the viral pp60(src). The possible roles played by the normal cell protein pp60(sarc) and the ASV transforming protein pp60(src) in normal cellular growth and neoplastic disease, respectively, are discussed.