Subgroup-specific antigenic determinants of avian RNA tumor virls structural proteins: analysis of virus recombinants.

Two nonglycosylated structural proteins of avian RNA tumor viruses, p15 and p19, were examined for the presence of subgroup-specific antigenic determinants by using competition radioimmunoassays. A comparison of viruses from subgroups A, B, and C revealed that subgroup B and C virus proteins were equally efficient in inhibiting the homologous radioimmunoassays which used antiserum against B77 and iodinated p15 and p19 from B77. On the other hand, subgroup A virus proteins were less efficient than subgroup C viruses in causing inhibition in these assays. That these differences in inhibition were due to true immunological differences was confirmed by using heterologous competition radioimmunoassays. Since it was possible to distinguish the p19 or p15 of subgroup A viruses from the corresponding proteins of either subgroup B or subgroup C virus, recombinant viruses from crosses between leukosis viruses of subgroup A and sarcoma viruses of subgroups B or C were examined. The recombinant viruses have the envelope glycoprotein gene (env) of the subgroup A virus and the sarcoma gene (src) of the subgroup B or C virus. The results show that 14 clones out of 17 examined had p19 from the sarcoma virus. RNA fingerprinting has shown that the src gene is located close to the 3′ end of the genome and is closely followed towards the 5′ end by the env gene. The observed linkage between src and p19 can be explained by postulating that the gene for p19 is located close to the 5′ end of the genome and that recombination takes place between circular forms of the virus genome.