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Effect of Protein Intake on Ribonucleic Acid Metabolism in Liver Cell Nuclei of the Rat¹

Institute of Biochemistry, The University, Glasgow,Scotland

Liver cell nuclei were isolated from 3 groups of rats, 1) animals that had been fed a protein-free diet, 2) animals in the post-absorptive state after receiving a diet of adequate protein content, and 3) animals actively absorbing amino acids from a recent meal of protein. The nuclei were fractionated by successive extraction with a phosphate buffer and M NaCl, leaving a "nucleolar" residue. Determinations of RNA in whole liver nuclei and their subfractions showed significant effects of protein intake. In the protein-depleted group, there was a reduction in the amount of RNA extractable with phosphate buffer and with M NaCl, and an increase in the RNA content of the nucleolar residue (group 1 vs. group 2). Two hours after feeding protein to fasting rats (group 3 vs. group 2), the total RNA content of the nucleus increased significantly. This was associated with a large increment in the amount of RNA in the nucleolar residue. However, the feeding of protein reduced the relative uptake of adenine-C¹⁴ into nucleolar RNA, indicating that the extra RNA in the nucleolar residue was of low metabolic activity. Protein feeding also caused a marked increase in adenine-C¹⁴ uptake by the RNA of the M NaCl extract. Attempts to identify dietary effects on the amounts of different molecular species of nuclear RNA by sedimentation analysis led to equivocal results.

Manuscript received 3 December 1964.