Control of Expression of Tumor Virus Genes in Uninfected Chicken Cells

The observation that sequences of tumor virus DNA can exist in an integrated state in the host chromosome helps to explain many early findings which suggested a vertical transmission of neo-plastic diseases. With a wide variety of animal systems, evidence has been accumulated for the existence of viral genetic information in cells of uninfected normal animals. Thus one of the central issues in tumor virus research is the question of possible regulatory mechanisms that control the expression of these viral genes. Studies on chicken cells have shown the existence of at least one control mechanism regulating the expression of a large portion of the viral genome (Payne and Chubb 1968; Weiss and Payne 1971; Hanafusa et al. 1974). In addition, however, cell types have been identified which exhibit differ-ential levels of expression of certain viral products and functions (Hanafusa et al. 1974). These data are suggestive of additional, more specific, mecha-nisms that control individual genes or groups of genes. The experiments described below were per-formed to evaluate the extent o which these varying levels of viral expressions are determined by regulatory genes or by differences in structural genes. Data will also be presented that demonstrate the genetic relationship between endogenous and exogenous viral genes. Techniques of nucleic acid hybridization and radioimmunoassay have been used to determine the specific gene sequences and the synthesis of individual viral proteins.