Induction of avian tumor viruses in normal cells by physical and chemical carcinogens

Avian tumor viruses were induced in normal chicken cells treated with ionizing radiations or chemical carcinogens and mutagens. The induced leukosis viruses possess a buoyant density, DNA polymerase, polypeptides, and 70S RNA typical of avian tumor viruses. Induced leukosis viruses act as helper agents for the defective Bryan high titer strain of Rous sarcoma virus and with one exception belong to subgroup E as judged by host-range, interference, and neutralization patterns. Induction of leukosis viruses was successful in chicken cells lacking the “natural” group specific (gs) antigen of the avian tumor viruses as well as in cells carrying this antigen. This observation indicates that the viral genome is present in gs⁺ and in gs⁻ cells. Therefore, the chromosomal locus which controls the presence of natural gs antigen in chicken cells does not represent the viral genome itself but regulates its expression in normal cells. These findings have implications for the origin of RNA tumor viruses and for theories of carcinogenesis.