Studies on free and membrane-bound ribosomes in rat liver: I. Distribution as related to total cellular RNA

Abstract

The distribution of RNA in rat liver has been determined to be: 80% ribosomal RNA, 15% non-sedimentable RNA, and 4 to 5% nuclear RNA. Ribosomal RNA which occurs in free ribosomes, not attached to membranes, has been found to amount to 20% of the cellular RNA. Membrane-bound ribosomes contain 60% of the cellular RNA. Both the ribosomal and non-sedimentable RNA fractions have been characterized in terms of their sedimentation profiles in sucrose gradients. The amount of RNA per mg DNA in fed rats is increased over the amount found in fasted rats; however, the distribution of RNA among the fractions studied is not significantly different between fasted and fed rats. There are approximately 6 × 10 6 ribosomes per average liver cell in fed rats, with approximately 10 molecules of non-sedimentable RNA per ribosome.