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³²P-Distribution in Oligonucleotides of Rapidly Sedimenting Nucleolar RNA's of Hepatomas and Normal Rat Liver¹

Department of Pharmacology, Tumor By-Products Laboratory, Baylor College of Medicine, Houston, Texas 77025

Nucleolar 28 S, 35 S, and 45 S RNA's were isolated from normal rat liver, Novikoff hepatoma ascites cells, and Morris hepatoma 9618A after short (60 min) and long (6 hr) labeling with orthophosphate-³²P. After purification by sucrose density sedimentation, the ³²P nucleotide composition of these RNA's was determined. The RNA was hydrolyzed to oligonucleotides with pancreatic ribonuclease. The distribution of radioactivity in the oligonucleotides was analyzed after they were separated by electrophoresis and chromatography.

In both the 60-min and the 6-hr labeling experiments, the distributions of the isotope in the oligonucleotides of nucleolar 28 S, 35 S, and 45 S RNA were virtually identical in any given tissue studied. The distributions of the isotope in the oligonucleotides in the nucleolar RNA's of normal liver were very similar in many respects to those in the tumors. However, in both the short and long labeling experiments, the isotope content of dinucleotides (mainly GC, the dinucleotide of guanylic and cytidylic acids, and GU, the dinucleotide of guanylic and uridylic acids) from both tumors was significantly higher than in the RNA of normal liver. The isotope content of the trinucleotides and tetranucleotides of the tumor RNA's were lower than those of the liver RNA's.

¹ This work was supported by the Cancer Center Grant No. CA-10893-01, the American Cancer Society Grant No. P/339 D, and the Jane Coffin Childs Fund.

Received 12/30/68. Accepted 6/ 5/69.