Stimulation of the synthesis of ribosomal proteins in regenerating rat liver with special reference to the increase in the amounts of effective mRNAs for ribosomal proteins.

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1 Normal and partially hepatectomized rats were pulse labeled for 15 min with [14C]leucine and [3H]leucine respectively. Both kinds of liver homogenates were mixed and the ribosomal protein fraction was purified from the mixed homogenate by chromatographic procedures. The 3H/14C ratio of this fraction was about three times higher than that of total protein, indicating that the synthesis of ribosomal proteins is selectively increased in regenerating rat liver. 2 The free polysomes from normal or regenerating rat livers were incubated with [3H]leucine in the presence of regenerating rat liver supernatant. Ribosomal proteins were then purified, finally by two-dimensional acrylamide gel electrophoresis. Biosyntheses of most of ribosomal proteins by regenerating rat liver polysomes were about 2.5 to 3.6 times higher than those by normal rat liver polysomes. 3 Using a wheat germ cell-free system, the template activities of poly(A)-containing mRNAs for ribosomal proteins were compared between normal and regenerating rat livers. The template activities at 6, 12, 18, 24 and 48 h after partial hepatectomy were about 1.3, 1.8, 2.4, 1.5 and 1.3 times higher, respectively, than the activity of normal rat liver. The extents of increase in the template activity of poly(A)-containing mRNAs for most of individual ribosomal proteins separated by two-dimensional gel electrophoresis were not so different at 18 h after the operation and the average template activity was 2.8 times higher than that of normal rat liver. The enhanced activity of regenerating rat liver for ribosomal protein synthesis is mainly caused by the increase in the apparent concentrations of mRNAs for ribosomal proteins.