Base composition of RNA fractions of nuclei of Walker tumor isolated with the citric acid procedure.

RNA was extracted from tumor nuclei isolated with the citric acid procedure. The RNA was subfractionated with phenol, and fractions of differing sedimentation constants were separated on sucrose density gradients. Each peak was refractionated by repeated sucrose density gradient centrifugaron until a sym metric peak was obtained. After phenol fractionation, the interphase or iRNA obtained by extraction at 65°Chad a higher uptake of orthophosphate-32P and larger amounts of rapidly sedimenting RNA than the aRNA fraction obtained after ex traction at room temperature. The individual peaks of RNA had characteristic base composi tions. The 6 S peak of the iRNA had a high content of adenylic and uridylic acids as determined both by optical density and 32Panalyses. It differed from the 6 S peak of the aRNA which contained more guanylic and cytidylic acid. As has been found for ribosomal RNA, nuclear 18 S RNA had a higher content of both adenylic and uridylic acids than 28 S RNA. The 35 S and 45 S fractions of iRNA and aRNA had a high content of guanylic and cytidylic acids as determined both by ultraviolet and MP analysis. The finding that the content of adenylic and uridylic acids of the 35 S and 45 S RNA of tumor nuclei was markedly lower than that of nuclei of rat liver supports previous studies which showed marked differences of the base compositions of newly synthesized rapidly sedimenting nuclear RNA of the Walker tumor and liver (19).