Isolation and initial characterization of nucleolar fibrillar remnants from the liver of rats treated with d-galactosamine

Abstract

Administration of d-galactosamine (250 mg/kg body weight) to rats causes a rapid and complete block of transcription. Within 4 h the granular components of nucleoli disappear, while the fibrillar components are condensed and converted into fibrillar remnants. The amount of precursors to rRNA (pre-rRNA) and rRNA components (mostly 28S rRNA) is reduced to less than 10% of that in control nucleoli. Electron microscopic radioautography shows also that the nucleolar fibrillar remnants do not contain pre-rRNA in growth-arrested transcription complexes. The Ag-staining reaction, adapted for electron microscopy, is positive with the fibrillar components of nucleoli. After d-galactosamine, the positive Ag staining is associated exclusively with the nucleolar fibrillar remnants. The positive Ag staining and the presence of rRNA genes, as revealed by rRNA:DNA hybridization, show that the nucleolar fibrillar remnants contain nucleolus organizer components. The fraction of nucleolar fibrillar remnants, isolated from nuclei of d-galactosamine-treated rats, preserves its ultrastructural characteristics observed in situ. It contains mainly DNA and proteins, including histones and nucleolar matrix proteins. The implications of these results for the elucidation of structural-biochemical correlations in the nucleolus are discussed.