Studies on Nucleolar RNA Fractions of the Walker and Novikoff Tumors¹

Following separation of various sedimentation classes of nucleolar RNA on linear sucrose gradients, they were analyzed for UV and ³²P base composition. The nucleolus of the Walker tumor contained mainly 6 S, 28 S, 35 S, 45 S, and 55 S RNA's; occasionally a small shoulder of 18 S RNA was found. After a 15-min pulse of orthophosphate-³²P, most of the radioactivity appeared in the 45 S and 55 S regions. Analysis of base composition of newly synthesized nucleolar 45 S RNA of the Walker tumor by distribution of orthophosphate-³²P showed that the content of adenylic acid was very low (13%); this result is similar to the ³²P base composition of the nucleolar RNA of the Walker tumor previously reported (10). By UV base analysis, the 6 S RNA had a higher content of adenylic and uridylic acid than the more rapidly sedimenting nucleolar RNA fractions. There were marked differences between the values obtained for base composition of newly synthesized nucleolar RNA of the Walker tumor and of normal liver. The 6 S nucleolar RNA of the Walker tumor also had a significantly different UV base composition from that of the normal liver.

When labeled nucleolar 45 S RNA of the Novikoff hepatoma was fractionated by partition chromatography on Sephadex G-25 using a biphasic organic solvent system, 10 radioactive fractions were obtained. By analysis for ³²P distribution in the nucleotides, it was found that those fractions with the highest content of adenylic acid were eluted first and those fractions with the lowest content of adenylic acid were eluted last.