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Influence of Toyocamycin on RNA Synthesis in Chick Embryo Cells Noninfected and Infected with Strain MC29 Avian Leukosis Virus¹

J. iman², L. Sverak, A. J. Langlois, R. A. Bonar and J. W. Beard

Department of Surgery, Duke University Medical Center, Durham, North Carolina 27706

Earlier studies showed that infection of chick embryo cells (CEC) by strain MC29 avian leukosis virus resulted in virus elaboration and a rapid, uniform morphologic alteration of the cells. No marked difference in the RNA synthesis patterns of infected and noninfected cells could be shown by the use of radioisotope-labeled RNA precursors and density gradient analysis. Treatment of the cultures with actinomycin D (AD) did not reveal any AD-resistant RNA synthesis related to virus infection. After treatment with toyocamycin (TCM), however, RNA synthesis in infected cells differed notably from that in noninfected cells. CEC infected with the MC29 virus and treated with low concentrations (0.1 to 0.2 µg/ml) of TCM showed reduced incorporation of labeled precursors into RNA in the 18 S and 4 S regions in comparison with noninfected cells. A much higher concentration of TCM (15 µg/ml) inhibited 28 S RNA formation almost completely, with substantial inhibition also of 18 S and 4 S RNA. With this high TCM concentration, the virus-infected CEC showed much higher rates of synthesis of RNA in the range of 45 S, 32 S, and 28 S than did the noninfected cells. RNA of about 18 S was also increased somewhat, and there were dramatic increases in 4 S RNA labeling. The differences were first marked between 14 and 24 hr after infection. Analysis of isolated nucleoli showed that incorporation of labeled precursors into nucleolar RNA of infected cells was 3-fold higher than into that of noninfected CEC. The effects of TCM on noninfected CEC differed significantly from those reported by others on mouse fibroblasts and other mammalian cells, particularly in the extensive conversion of 45 S to 32 S ribosomal RNA precursor in CEC, a marked TCM-resistant labeling of 18 S RNA, and a lower overall sensitivity of CEC RNA synthesis to the drug. The characteristics of the virus-related changes in RNA metabolism seen in the presence of toyocamycin and their possible significance are discussed.

¹ This investigation was supported by USPHS Grant C-4572; by the Annie Mabel Sherris Memorial Grant for Cancer Research from the American Cancer Society, Inc.; and by the Dorothy Beard Research Fund.

² Visiting professor, Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Science, Prague, Czechoslovakia.

Received 11/19/68. Accepted 4/ 6/69.