Thioacetamide, administered in a dose of 50/mg/kg for 9 days, produced a profound effect on the distribution and labeling of ribonucleic acid (RNA) of the rat liver. The amount of p-RNA (released by phenol into the aqueous phase) and r-RNA (which remained in the phenol), was increased two- to threefold in the nuclei. In the nucleoli, the amount of p-RNA was doubled, and the r-RNA was increased by a factor of 3.5. The amount of mitochondrial and microsomal RNA was correspondingly decreased, but the p-RNA of the cytoplasmic sap was increased. Thioacetamide suppressed the incorporation of orotic acid-2-C14 into the p- and r-RNA of the nuclei. As measured by specific activity, the labeling of nucleolar p-RNA was unchanged by thioacetamide. The labeling of the r-RNA of the nucleoli was suppressed by 30 per cent at early time points.

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Supported by grants from the U.S. Public Health Service, Jane Coffin Childs Fund, the American Cancer Society, and the Anna Fuller Fund.

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