Association of the transforming proteins of the ST and GA strains of feline sarcoma virus and their in vitro associated protein kinase activities with cellular membranes.

The translation products of the Snyder-Theilen (ST) and Gardner-Arnstein (GA) strains of feline sarcoma virus (FeSV), termed gag-fes proteins, are high molecular weight polyproteins containing different amounts of the amino terminus of the feline leukemia virus (FeLV) gag gene-coded precursor protein linked to a similar sarcoma virus-specific polypeptide. Both polyproteins are phosphoproteins with indistinguishable in vitro associated tyrosine-specific protein kinase activities. The polyproteins are extremely hydrophobic proteins which are intimately associated with the plasma membrane fraction of transformed cells. Approximately 10% of the proteins are modified by glycosylation and expressed on the cell surface where they are accessible to lactoperoxidase-mediated radio-iodination and trypsinization. Cell surface localization of the polyproteins does not appear to be necessary for transformation. However, preliminary evidence suggests that the amount of FeLV p30 sequences at the amino end of the proteins may have some effect on the intracellular distribution of the gag-fes polyproteins and on the phenotype of the transformed cell.