Metabolism of RNA in the liver cells of the rat II. Chemical analysis of RNA in cellular components

Abstract

RNA was extracted with the SDS phenol procedures from cytoplasmic and nucleolar fractions and with phenol from chromatin and nuclear sap fractions. The RNA species in these cellular components were analyzed by the sucrose density gradient centrifugation and gel filtration Sephadex G-200 column. Nucleotide compositions of RNA fractionated by these methods were also studied. Cytoplasmic RNA consisted of 28 S, 18 S ribosomal and 4 S soluble RNA but very small amounts of intermediate molecular-sized RNA. Nucleolar RNA contained a large amount of heterogeneous molecular-sized RNA between 28 S and 18 S. Chromatin and nuclear sap RNA was characterized by the presence of a large amount of intermediate molecular-sized RNA between ribosomal and soluble RNA. Ribosomal RNA had a high content of guanylic and cytidylic acid but intermediate molecular-sized RNA had a relatively high content of adenylic and uridylic acid. The relative amounts of ribosomal, intermediate molecular-sized AU-rich and soluble RNA were 75, 0, 25 per cent for cytoplasm, 37.3, 26.9, 35.8 per cent for chromatin, 39.2, 22.5, 38.3 per cent for nuclear sap and 70.0, 19.5, 10.5 per cent for nucleolar RNA. Thus, cytoplasmic and nucleolar RNA were characterized by being GC-rich, but chromatin and nuclear sap by intermediate molecular-sized RNA, AU-rich. The results of the base analysis of nuclear components indicated that nucleolar RNA was about 25 per cent of total nuclear RNA.