The ribonucleoprotein particles were isolated from livers of rats fed basal and 4-dimethylaminoazobenzene (DAB) diets, from DAB-induced primary tumors and from Novikoff hepatoma. The results showed that the protein and ribonucleic acid contents of the ribosomal fraction decreased equally in both basal- and DAB-fed rats after seven weeks of feeding, and returned to normal levels after 23 weeks. The levels of these components were slightly higher in the primary and transplanted tumors.

The level of ribonuclease activity decreased in both the basal- and DAB-fed rats for 7 weeks. Though the RNase activity returned to a normal level in the basal diet-fed rats, a progressive decrease was observed in the DAB-fed rats. No activity could be detected after 23 weeks of DAB feeding. A total loss in the enzymatic activity was also noticed in the ribonucleoprotein particles isolated from DAB-induced and transplanted tumors.

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This investigation has been supported by grants from the National Cancer Institute of Canada, the Damon Runyon Memorial Fund for Cancer Research Inc., and the Medical Research Council of Canada to Dr. A. Cantero, director of the Research Laboratories.

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