Uninfected avian cells contain RNA related to the transforming gene of avian sarcoma viruses

Abstract

A single gene ( src) is responsible for neoplastic transformation induced by infection of fibroblasts with avian sarcoma viruses. We have reported previously that the DNAs of uninfected avian cells contain nucleotide sequences related to src, and that these sequences (denoted sarc) have been highly conserved during the evolution of birds (Stehelin et al., 1976b). We now demonstrate that sarc is transcribed into RNA in a variety of normal and neoplastic avian cells and tissues, including cultured embryonic fibroblasts, normal embryos, normal adult tissues, fibrosarcomas induced by chemical carcinogens and cells explanted from these tumors into continuous culture. Since we detect no transcription from the genes for globin and ovalbumin in embryonic avian fibroblasts, we conclude that the presence of sarc RNA in normal cells cannot be attributed to a low constitutive level of transcription from all cellular genes. The amounts of sarc RNA are similar in normal and neoplastic cells, in embryos at all periods of development, and in both logarithmically growing and fully quiescent fibroblasts. Synthesis of sarc RNA in chicken cells is not coordinated with the expression of endogenous retrovirus genes; this finding conforms to other evidence that sarc is not linked to an endogenous viral genome. In the accompanying manuscript, we describe the characteristics of sarc RNA in normal and neoplastic avian cells, and we conclude that sarc is part of a large messenger RNA in both types of cells. Our data fail to implicate the expression of sarc in normal cellular growth, embryogenesis or chemical carcinogenesis, and the function of sarc remains unknown.