Characterization of a 105,000 molecular weightgag-related phosphoprotein from cells transformed by the defective avian sarcoma virus PRCII

In cells infected with the replication-defective avian sarcoma virus PRCII a single virus-specific product is detectable, a polyprotein of 105,000 molecular weight (p105). P105 can be precipitated with antisera togag proteins of avian leukosis and sarcoma viruses. By two-dimensional tryptic peptide analysis of [35S]methionine-labeled proteins we have shown that p105 contains peptides of helper viriongag proteins p19 and p27, but not of p15. In addition a number of peptides are present in p105 that are not found in any of the helper virus gene products including gPr95env and Pr180gag-pol. These p105-specific peptides are not detectable in the p60src protein of Rous sarcoma virus (RSV) nor in thegag-related polyproteins encoded by avian myelocytoma and carcinoma viruses MC29 and MH2 or avian erythroblastosis virus AEV. P105 is not detectably glycosylated, but is heavily phosphorylated. In this respect it resembles p60src of RSV rather than the polyproteins of avian leukemia viruses. Since p105 is the only viral gene product detectable in nonproducing cells transformed by PRCII, this protein may be important in the initiation and maintenance of oncogenic transformation. The nonstructural sequences in p105 would then represent a new class of transforming gene in avian oncoviruses