Phosphorus incorporation into nucleic acids and proteins of liver nuclei of normal and azo dye-fed rats.

It has been known since the work of Marshak (13) that nuclear ribonucleic acid (RNA) incor porates @82 at a much greater rate than cyto plasmic RNA. This has been confirmed by a num ber of investigators (@,10). Griffin and co-workers (7) showed that nuclear RNA, as obtained by the Schmidt and Thannhauser fractionation method (17), was more active in its rate of uptake of @32 in azo dye-induced hepatomas than in a similar fraction from normal liver. Furthermore, these workers were able to show that the rate of phos phorus incorporation in the livers of precancerous animals was similar to that in tumor tissue in all fractions studied. (The term “precancerous―was used to indicate those animals which had been fed a diet containing 0.06 per cent of the dye S'-methyl-4-dimethylaminoazobenzene (8'-Me DAB) for 6-8 weeks but had not developed any liver tumors, since this usually requires 1@—15 weeks.) Subsequent work by Ward et al. (@1) showed that agents which delayed the carcinogenic process also depressed the rate-of phosphorus up take in precancerous animals but did not com pletely restore the metabolic pattern to normal levels. In the work cited above for precancerous and cancerous animals, the Schmidt and Thannhauser method of fractionation was employed to isolate the various phosphorus-containing fractions. Since it is well known that this method of fractionation introduces some contamination of the RNA frac tion by inorganic phosphate released from phos phoprotein during the alkaline degradation of