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Effect of Rous Sarcoma Virus Infection on Recovery of Nucleolar RNA, Ribonucleoprotein, and DNA Synthesis from Inhibition by Actinomycin D¹

Laboratory of Experimental Pathology, National Institute of Arthritis and Metabolic Disease, and Viral Biology Branch, National Cancer Institute, NIH, Bethesda, Maryland 20014

The effect of Rous sarcoma virus (RSV) infection on the recovery of nucleolar RNA and protein synthesis from selective inhibition by actinomycin D was investigated using radio-autographic technics. A transient increase in the grain count over nucleoli of actinomycin-treated cells, pulse-labeled with tritiated uridine, was observed in cells 10 to 18 hours after infection with Bryan strain RSV. The proportion of the total RNA synthesized in the nucleolus at that time is greater than in infected or uninfected cells not treated with actinomycin. In mock-infected cells, or in cells exposed to inactivated virus, inhibition of nucleolar RNA synthesis persists for 24 hours after removal of the inhibitor. During this period, actinomycin inhibits both the accumulation of protein label in the nucleolus as well as cellular DNA synthesis, and this inhibition is identical in infected and in uninfected cells. However, 48 to 72 hours after infection, a period coincident with the appearance of some transformed cells, DNA synthesis is significantly greater in infected cells not previously inhibited by actinomycin than in uninfected cells, whether actinomycin-treated or not. It is therefore concluded that RSV infection directly results in the transient synthesis of a nucleolar RNA that is not inhibited by actinomycin under these conditions, whereas the concomitant synthesis of nucleolar protein and cellular DNA is inhibited. The possible relationship of these findings to the formation of the mature virus particle and to the development of transformation is discussed.

¹ Presented in part at the Fifty-second Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey, 1968. Federation Proceedings 27: 2801,1968.

² Present address: Laboratoire de Médecine Expérimentale, Collège de France, 11 Place Marcelin Berthelot, 75 Paris, 5 ème, France.

Received 9/ 3/68. Accepted 4/22/69.