Transforming proteins of some feline and avian sarcoma viruses are related structurally and functionally.

Transformation of chicken cells by Fujinami sarcoma virus (FSV), PRC II or Y73 (three independently isolated avian sarcoma viruses that are replication-defective and lack the Rous sarcoma virus src gene) resulted in significant elevation (4-13 fold) of phosphotyrosine levels in cellular protein. The gag-related proteins encoded by these avian sarcoma viruses (ASVs) were all associated with tyrosine-specific protein kinase activity when assayed in immune complexes and were phosphorylated at both tyrosine and serine residues in vivo. Both the phosphotyrosine level in protein of FSV-infected cells and the protein kinase activity assayed in immune complexes containing the FSV protein P140 were temperature-sensitive. The presumed transforming proteins of these ASVs were compared with those of Rous sarcoma virus (RSV), Abelson murine leukemia virus and the Snyder-Theilen and Gardner-Arnstein strains of feline sarcoma virus (FeSV), which have previously been associated with tyrosine-specific protein kinase activity. FSV and PRC II proteins were shown to be structurally related to one another and to the FeSV proteins by tryptic peptide mapping and by immunological studies. No homology was observed, however, between the transforming proteins of RSV, Y73, Abelson murine leukemia virus and the FSV/PRC II/FeSV class, suggesting there may be at least four classes of retroviruses whose transformation mechanisms involve aberrant phosphorylation of cellular protein at tyrosine residues.