Common features of the base composition of rapidly labeled RNA of nucleoli in a number of experimental tumors.

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 doclecyl sulfate-phénolprocedure and fractionated by sucrose density (¡radientcentrifugation, 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 UNA fractions after pulse labeling for 10-20 min with orthophosphate-12? in vivo with the ascites cells and in vitro with the