Only membrane-associated RSV src proteins have amino-terminally bound lipid.

Abstract

The product of the Rous sarcoma virus (RSV) transforming gene, src, is a phosphoprotein of molecular weight (Mr) 60,000 (pp60src)1 that interacts with cellular membranes via an 8,000 Mr amino-terminal hydrophobic domain2–6, possibly after post-translational modification5,7,8. Recently, it has been demonstrated that fatty acid is tightly associated with some membrane-bound proteins9–15, including pp60src (ref. 16). The fatty acid attachment site is located within the membrane-embedded region of the vesicular stomatitis and Sindbis virus glycoproteins11,13–15. To test for a similar modification of the ammo-terminal domain of pp60src, we measured the incorporation of 3H-palmitic acid into pp60src of cells that had been transformed by wild-type RSV or recovered avian sarcoma viruses (rASVs)6,17, some of which have variant forms of pp60src. We report here that membrane-associated pp60src proteins encoded by either wild-type RSV or rAS V14416,17 contain bound lipid. However, pp60src proteins with amino-terminal size variations encoded by two different rASV isolates, rASV 157 and rASV 170217, that behave as soluble, cytoplasmic proteins6, contain no detectable lipid. Furthermore, we observed that lipid association is temperature sensitive in cells infected with RSV mutant tsNY6818, whose pp60src membrane association is temperature sensitive19–21. These data support the role of lipid binding in the membrane association of pp60src and suggest that the amino-terminal 8,000 Mr of pp60src contains the lipid attachment site.