Isolation, characterization, and stability of the 30S ribosomal RNA complex from HeLa cells

Immunocytochemical identification of nuclear structures containing snRNPs in isolated rat liver cells

Small nuclear ribonucleoproteins (snRNPs) containing U1, U2, U4, U5, and U6 small nuclear RNAs were detected by ultrastructural immunocytochemistry in the nuclei of isolated rat hepatocytes using Fab fragments of anti-Sm and anti-RNP autoantibodies. Their localization was carried out in normal cells and in cells treated with two drugs, the adenosine analog DRB and CdCl2, which alter the number and distribution of nuclear RNP components. It was found that more precise determination of the distribution of these small RNAs could be obtained by using two complementary procedures in parallel rather than either one alone. They consisted of an indirect immunoperoxidase labeling carried out before embedment and an indirect immunogold labeling applied to thin sections of cells embedded in Lowicryl K4M. The results indicate that snRNPs are associated with all extranucleolar perichromatin fibrils and granules and interchromatin fibrils, which confirms that they occur in structures involved in the synthesis and processing of hnRNA. The snRNPs are not associated with nucleolar perichromatin granules induced by DRB, which confirms that there may be two kinds of perichromatin granules. The snRNPs are also associated with the still enigmatic interchromatin granules which apparently do not contain hnRNA but at least in DRB-treated cells, also contain ribosomal RNA.

Regulation of mitochondrial ribosomal RNA synthesis in yeast. I. In search of a relaxation of stringency

Studies were undertaken to determine if mitochondrial rRNA synthesis in yeast is regulated by general cellular stringent control mechanism. Those variables affecting the relaxation of a cycloheximide-induced stringent response as a result of medium-shift-down or tyrosine limitation include: 1) the stage of cell growth, 2) carbon source, 3) strain differences and, 4) integrity of the cell wall. The extent of phenotypic relaxation decreased or was eliminated entirely in a strain dependent manner as cells entered stationary phase of growth or by growth of cells on galactose or in osmotically stabilized spheroplast cultures. Cytoplasmic and mitochondrial RNA species were extracted from regrowing spheroplast cultures subjected to different experimental regimens and analyzed by electrophoresis on 2.5% polyacrylamide gels. Relative rates of synthesis were determined in pulse experiments and normalized by double-label procedures to longterm label material. Tyrosine starvation was found to inhibit synthesis of the large and small rRNA species of both cytoplasmic and mitochondrial rRNAs to about 5-20% of the control values. Chloramphenicol inhibits mitochondrial and cytoplasmic rRNA synthesis to 60-80% of control; however, chloramphenicol addition does not relax the stringent inhibition of either class of rRNAs. Cycloheximide addition results in 70-80% inhibition of synthesis of both cellular speceis of rRNAs. As noted above, cycloheximide does not relax the stringent response of cytoplasmic rRNA synthesis in spheroplasts, and also does not relax the stringent inhibition of mitochondrial rRNA synthesis. From these studies, we conclude that both cytoplasmic and mitochondrial rRNA synthesis share common control mechanisms related to regulation of protein synthesis by shift-down or amino acid limitation.