Tyrosine Phosphorylation Sites Common To Transforming Proteins Encoded By Gardner And Snyder-Theilen Fesv

The Gardner and Snyder-Theilen strains of feline sarcoma virus (FeSV) encode 110,000 molecular weight ( M r ) polyproteins as their primary translational products. Cells transformed by a variant of Snyder-Theilen FeSV express an 85,000 M r polyprotein. Single tyrosine phosphorylation sites identified within each of these viral gene products are shown to represent major in vitro acceptors phosphorylated by the polyprotein associated protein kinases. By two-dimensional tryptic peptide analysis, these acceptor sites are highly related although exhibit minor differences in map position, while by analytical high-performance liquid chromatography, all three elute at approximately the same acetonitrile concentration (21–23%). The tyrosine acceptor sites in these FeSV-encoded polyproteins have been localized by sequential Edman degradation at a position seven amino acid residues distal to their trypsin cleavage site. The major tyrosine acceptors, two serine phosphorylation acceptors common to the p12 structural components of all three polyproteins, a single major phosphothreonine site, and several minor less well-resolved acceptor sites are shown to be phosphorylated in vivo . In addition to the major tyrosine acceptor site initially phosphorylated in vitro , phosphorylation of secondary tyrosine acceptors is shown to occur to proportionately greater extents when in vitro phosphotransferase reactions are carried out for longer times or at higher temperatures.