Quantitative Determination of the Ribosomal Ribonucleic Acid Content of Liver and Novikoff Hepatoma from Fed and from Fasted Rats

Although never demonstrated unequivocally, it has been generally accepted that the largest fraction of the ribonucleic acid of mammalian cells is ribosomal. However, it has been reported recently that about 65% of rat liver RNA has a nonribosomal sedimentation coefficient in the range of 4 S. To resolve the question of the ribosomal RNA content of rat liver and to examine the validity of the assumption that the total RNA content of mammalian tissue can be taken as an approximate measure of ribosome content, isotope dilution analysis has been used in the present study for quantitative determination of ribosomal RNA, since this technique yields valid minimal values in this application. These measurements indicate that, of total rat liver RNA, the ribosomal fraction constitutes 85 to 90%, and 4 S RNA, about 7%. The fraction of ribosomal RNA relative to the total remained unchanged despite a period of fasting sufficient to reduce the RNA per hepatic cell to about half the normal value. A rapidly growing neoplasm, the Novikoff hepatoma, was found to contain the same amount of ribosomal RNA, relative to total, as did the liver.