Effects of the inhibition of ribosomal-RNA synthesis on the synthesis of ribosomal structural proteins in regenerating rat liver.

Abstract

Employing regenerating rat liver, the metabolic coordination between ribosomal RNA and ribosomal proteins was investigated. 1 When the synthesis of ribosomal RNA was selectively inhibited by a low dose of actinomycin D, the incorporation of labeled amino acid not only into protein components of cytoplasmic ribosomes but also into those of nucleolar 60-S particles were markedly decreased. The inhibition was rather selective. 2 The ribosomal protein fraction (Fraction I) was purified from the acid-soluble proteins of total cell homogenate by CM-cellulose column chromatography. Fraction I showed many bands with the same mobilities as those of ribosomal structural proteins on acrylamide gel electrophoresis. Actinomycin D treatment for 5 min to 1 h inhibited the incorporation of labelled amino acids into Fraction I and its subfractions on acrylamide gel electrophoresis. The maximal level of inhibition was obtained by the actinomycin D treatment for 20 min. 3 Acrylamide gel electrophoresis of Fraction I, prepared from nascent protein fractions of rat liver ribosomes pulse-labeled with amino acids, showed that the incorporation into nascent ribosomal proteins was inhibited by the actinomycin D treatment for 1 h. 4 It is indicated that the biosynthesis of the bulk of ribosomal proteins itself may be coordinated with that of ribosomal RNA in regenerating rat liver.