Unifected avian cells contain structurally unrelated progenitors of viral sarcoma genes.

A single gene, src of Rous sarcoma virus (RSV) coding for a protein of pp60src, is responsible for the transformation of fibroblasts. DNA sequences homologous to src (the endogenous sarc) are presented in uninfected cells of chickens and other vertebrates. Endogenous nucleotide sequences have also been found in the putative transforming genes of MC29 (ref. 6) and avian erythroblastosis virus. These viruses, however, induce different spectra of tumours in animals. From analysis of a new avian sarcoma virus, Y73, we present here evidence suggesting that multiforms of viral sarcoma genes originated from cellular genetic sequences, and that these viral genes are structurally unrelated, but have similar pathogenicities.