[Intranuclear distribution of rat liver ribosomal RNA]

A method is described for the isolation of pure liver nuclei with minimal cytoplasmic contaminants, loss of nuclear RNA and degradation of nuclear RNA. The RNA components are extracted in three distinct fractions by subsequent treatment with phenol at 4 degrees, 50 degrees and 85 degrees C. The total and 14C-orotate labelled RNA components in the three nuclear RNA fractions are characterized by nucleotide composition, poly(A)-RNA content and agar-gel electrophoresis. The results show that the RNA in three fractions correspond to the nucleosol, nucleolus and chromatin compartments of the nucleus. The nuclear HnRNA components are exclusively in the 85 degrees C RNA. Nuclear ribosomal RNA is extracted in the 4 degrees C and 50 degrees C RNA fractions. These two nuclear RNA fractions are distinct in constituent pre-rRNA species and the rate of labelling of their rRNA components. The amount of the pre-rRNA and rRNA species is determined. The results show that the nucleolus-nucleosol and nucleosol-cytoplasm transitions of ribosomal subparticles are markedly slower processes than the preceeding steps of ribosome biogenesis.