Oncogene and its production of an avian sarcoma virus Y73

The Y73 strain of avian sarcoma virus isolated from a transplantable chicken tumor was defective in its replicating capacity. The virus caused sarcoma but not acute leukosis in chickens even when inoculated intravenously. It induced transformed cell-foci in cultured fibroblasts and the viral genome responsible for in vitro transformation was 26S RNA. The RNA was composed of sequences in common with helper virus RNA and Y73-specific sequence. The specific sequence "yes" did not hybridize with complementary DNA to the src gene of Rous sarcoma virus (cDNAsrc) and it had a unique counterpart in normal cell DNA. The yes gene was located in the middle of the 26S genome and the sequences common to the helper virus were located toward both ends. The 26S RNA coded for an polyprotein of 90,000 daltons (p90) which included p19 of viral core proteins in addition to the polypeptide unique to the yes gene. p90 had protein kinase activity specific for tyrosine residue and itself could be phosphorylated at tyrosine residue in vivo and in vitro, and at serine residue in vivo.