Studies on the reproductive and cell-converting abilities of avian sarcoma visuses

Abstract In order to study whether or not only a part of the genome of avian sarcoma viruses (ASV) is sufficient for focus formation and/or for virus reproduction we attempted to isolate two classes of ASV mutants. A search was made for virus particles which have lost their ability to reproduce but are still able to convert chicken cells; and particles which have lost their ability to convert cells but are still able to reproduce. Particles of the first class were not found. Single foci induced by three ASV strains treated with either hydroxylamine, 60 Co-γ-, X-, or UV-rays all produced converting virus. Another ASV strain studied (B77 virus) was exceptional in that hydroxylamine-treated virus induced foci which regressed after subsequent subcultivations. Although these foci revealed no virus detectable in the focus assay, electron microscopic studies showed the presence of C-type particles. In addition three low virus-producing mutants were isolated from the B77 strain, one of which induced the formation of regressing foci. Mutants of the second class were found which, although infectious, do not convert chicken embryo fibroblasts. These nonconverting mutants were obtained from ASV strains of subgroups A and D and have envelope properties similar to their corresponding sarcoma virus strains. A tentative model for the genome of avian sarcoma viruses is proposed. Whereas the whole genome of ASV is needed for the induction of proliferating foci only a part of it is sufficient for the production of virus particles.