A rapid and sensitive method for measuring ribonucleic acid in ribosomal preparations

9-Aminoacridine Inhibits Ribosome Biogenesis by Targeting Both Transcription and Processing of Ribosomal RNA

Aminoacridines, used for decades as antiseptic and antiparasitic agents, are prospective candidates for therapeutic repurposing and new drug development. Although the mechanisms behind their biological effects are not fully elucidated, they are most often attributed to the acridines’ ability to intercalate into DNA. Here, we characterized the effects of 9-aminoacridine (9AA) on pre-rRNA metabolism in cultured mammalian cells. Our results demonstrate that 9AA inhibits both transcription of the ribosomal RNA precursors (pre-rRNA) and processing of the already synthesized pre-rRNAs, thereby rapidly abolishing ribosome biogenesis. Using a fluorescent intercalator displacement assay, we further show that 9AA can bind to RNA in vitro, which likely contributes to its ability to inhibit post-transcriptional steps in pre-rRNA maturation. These findings extend the arsenal of small-molecule compounds that can be used to block ribosome biogenesis in mammalian cells and have implications for the pharmacological development of new ribosome biogenesis inhibitors.

The comparative content of the mitochondrial phosphoglyceroyl-ATP-containing polymer, purinogen, in rat tissues

Here, we describe an assay for the tissue content of purinogen, a highly phosphorylated labile polymer containing ATP and phosphoglycerate found in the mitochondrial intermembrane space. We report the purinogen content (as adenine nucleotide equivalents) of rat heart and, for the first time, of rat liver, kidney, brain and mixed skeletal muscle. The findings show that purinogen contains very significant proportions of cell adenine nucleotides ranging from 25% of the free pool in brain and skeletal muscle to 135% of it in kidney. The evidence that purinogen may form a controlled intracellular reservoir of inorganic phosphate is briefly discussed.

Fluorometric determination of DNA and RNA in Chlamydomonas using ethidium bromide

By using the fluorescence enhancement of ethidium bromide bound to nuclei acid, a very rapid, simple and sensitive assay of DNA in the green alga Chlamydomonas has been devised. Total fluorescence (DNA + RNA) was determined by complex formation with ethidium bromide in a cell lysate made by mixing cell samples with lauroyl sarcosinate, EDTA and NaOH and incubating the mixture for 5 min at room temperature followed by neutralization. For determination of DNA the RNA was digested by incubating the cell sample in te alkaline lysis solution for 45 min at 60 degrees C followed by neutralization, and complex formation with ethidium bromide. Quenching of the fluorescence due to cellular pigments was corrected for using an internal DNA standard.

Crystalline ribosomes are present in brains from senile humans

Paracrystalline inclusions known as Hirano bodies characteristically appear in the hippocampal region of the brains of humans exhibiting senile and presenile dementias as well as several other neurodegenerative diseases. We present evidence that the currently accepted model for those structures based on alternating filament sheets is not correct, but that Hirano bodies are stacked sheets of membrane-bound ribosomal particles derived from partially degraded rough endoplasmic reticulum or Nissl substance. Using fluorescence staining with acridine orange and ethidium bromide, were have shown that the bodies contain RNA. Spatial filtering of electron micrographs by Fourier techniques shows that the individual particles that make up the arrays have a characteristic shape previously reported for the large subunit of eukaryotic ribosomes. The storage of these ribosomal particles in inclusion bodies may indicate a quiescent state of protein synthesis in the cells. This withdrawal of synthetic mechanisms in the hippocampus may have significant consequences in the loss of ability to consolidate short-term to long-term memory.