A Quantitative Autoradiographic Study of Nucleolus-Associated RNA and DNA Synthesis During the Eclipse Phase in Rous Sarcoma Virus-Infected Chicken Fibroblasts

Functional and morphologic differences between the sensitivity of nucleoli of Rous sarcoma virustransformed cells and that of newly infected cells to the action of actinomycin D (AD) have been demonstrated by quantitative light and electron microscope autoradiography and utilized to investigate the function of the nucleolus in the early stages of infection. After a pulse exposure to low doses of AD, increased RNA synthesis is induced within 80 minutes in the fibrillar portion of the nucleolus by infection. A concomitant increase in the retention of tritiated AD in the nucleolus and a quantitative redistribution of intranuclear and cytoplasmic DNA label are interpreted as evidence for a virus-induced amplification of the binding sites of AD in nucleolar chromatin.