Enhanced transcription of c-myc in bursal lymphoma cells requires continuous protein synthesis.

In several bursal lymphoma cell lines in which c-myc transcription is regulated by avian leukosis virus (ALV) long terminal repeat (LTR) sequences, protein synthesis inhibition decreases the transcriptional activity of c-myc as well as other LTR driven viral genes. This decrease in transcription is associated with a change in the chromatin structure of c-myc, as measured by deoxyribonuclease I (DNase I) hypersensitivity, and a shift of transcription from the LTR to the normal c-myc promoter. In contrast, cycloheximide had little or no effect on the transcription of LTR driven genes in infected chicken embryo fibroblasts treated with the drug. These results suggest that a labile, cell type-specific protein may interact with the retroviral LTR and regulate transcription of genes under LTR control. Further, the results demonstrate that the increase in intracellular concentration of c-myc RNA induced by cycloheximide treatment of normal cells is the result of stabilization of this message.