After 120 min of incubation of labeled 18 S or 28 S RNA or the B3 fragment with Novikoff hepatoma ascites cells in the presence of diethylaminoethyl dextran, 60 to 70% of the isotope was cell associated, i.e., it cosedimented with the cells. Of this cell-associated RNA, the 18 S and 28 S RNA were degraded to approximately 10 S and 15 S fragments. Treatment of the cells with pancreatic RNase removed most of the cell-associated RNA fragments but, in each case, 4 S fragments remained cell associated; these were richer in guanosine 5′-phosphate and cytidine 5′-phosphate than the original RNA. These 4 S fragments contained approximately 28, 8, 6, and 2% of the isotope of the adsorbed B3 fragment and 18 S, 28 S, and 4 S RNA, respectively. A maximum of 1% of 4 S RNA and 5% of the 4 S fragments from other RNAs was intracellular.

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This work was supported in part by Cancer Center Grant CA-10893 P.1 and grants from Eli Lilly and Company and the DeBakey Foundation.

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