title: Cleavage of four avian sarcoma virus polyproteins with virion protease p15 removes gag sequences and yields large fragments that function as tyrosine phosphoacceptors in vitro.
abstract: The transformation-specific polyproteins of avian sarcoma viruses PRCII, PRCII-p, Fujinami sarcoma virus (FSV), and Esh sarcoma virus (ESV) consist of two domains, one derived from a partial viral gag gene and the other representing an apparently cell-derived insert in the defective viral genome. These gag-linked proteins were cleaved with retrovirion protease p15. Cleavage of PRCII-p polyprotein P170, P105 of PRCII, and P140 of FSV occurred within the gag domain and generated fragments of Mr 130,000, 70,000, and 115,000, respectively, containing all of the transformation-specific sequences linked to a remnant of the original gag sequences. ESV P80 was cleaved inside the transformation-specific domain, yielding a Mr 35,000--38,000 fragment from the NH2-terminal half of the molecule consisting of the entire gag portion and some no-gag sequences and a Mr 48,000 fragment containing most of the transformation-specific sequences. The tyrosine phosphorylation sites of the polyproteins were found in every case in the transformation-specific fragments. The major serine phosphorylation site of ESV P80 was found to reside in the Mr 35,000--38,000 gag-containing fragment, probably within the transformation-specific sequences of that cleavage product. Removal of all of the gag domain of ESV P80 or most of the gag domain in PRCII-p P170, PRCII P105, and FSV P140 does not affect their ability to be phosphorylated by the polyprotein-associated tyrosine-specific protein kinase activities. This observation suggests that the gag sequences of the polyproteins of classes II (PRCII-p, PRCII, and FSV) and III (ESV) avian sarcoma viruses may not be required for this enzymatic function, which appears to be of importance in transformation.
mesh_terms: D001355:Alpharetrovirus / Q000378:metabolism*; D002472:Cell Transformation, Viral; D015683:Gene Products, gag; D010446:Peptide Fragments / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine; D011494:Protein Kinases / Q000378:metabolism; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D015683:Gene Products, gag; D010446:Peptide Fragments; D010750:Phosphoproteins; D014764:Viral Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D011494:Protein Kinases; D010447:Peptide Hydrolases