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Common Features of the Base Composition of Rapidly Labeled RNA of Nucleoli in a Number of Experimental Tumors¹

Departments of Pharmacology, Virology, and Epidemiology, Baylor University College of Medicine, Houston, Texas 77025

Nucleoli were isolated by sonication and differential centrifugation from Novikoff hepatoma ascites cells, Ehrlich ascites cells, HeLa cells, and H-50 cells. RNA was extracted with the sodium dodecyl sulfate-phenol procedure and fractionated by sucrose density gradient centrifugation, which revealed that the nucleolar RNA could be fractionated into 4 major components with sedimentation constants of 6 S, 28 S, 35 S, and 45 S. The bulk of the radioactivity was found in the rapidly sedimenting RNA fractions after pulse labeling for 10–20 min with orthophosphate-³²P in vivo with the ascites cells and in vitro with the cultured cells. The peak of the radioactivity coincided with the 45 S peak in the optical density pattern.

The ³²P base compositions of the early labeled nucleolar 45 S RNA were quite similar in the various neoplastic tissues studied. The content of cytidylic acid was higher than that of the nontumor tissues studied. The content of adenylic acid was lower than that of normal and regenerating rat liver, but the rapidly labeled nucleolar RNA of monkey kidney also had a low content of adenylic acid similar to that of the tumors. In newly synthesized RNA of the monkey kidney, the content of uridylic acid was higher than that of either the tumors or the livers.

¹ These studies were supported in part by grants from the American Cancer Society, the Jane Coffin Childs Fund, the National Science Foundation and the USPHS (CA 08182).

² American Cancer Society Professor of Virology.

Received 11/ 7/66. Accepted 2/ 2/67.