Ribosomal Stability Research Articles

The chemical structure and stability of yeast ribosomes

1. 1. RNAase is associated with yeast ribosomes. The intact ribosomes were stable below 20°, showed no RNAase activity and their ribonucleic acid was resistant to RNAase. However, ribosome-bound RNAase was fully activated and released by incubation at 25°. Ribosomal RNA was denatured and became sensitive to RNAase during incubation at temperatures between 20° and 50°. 2. 2. Adenosine triphosphate was associated with ribosomes. During incubation, conversion of ATP to AMP and liberation of inorganic phosphate from ribosomes were observed. The heat-denaturation of the RNA in ribosomes as measured by hyperchromicity could be reversed by the addition of an ATP-generating system. 3. 3. At 37° the ribosomes were unstable in buffered solution containing 2 mM Mg 2+ but were stabilized by the addition of ATP and spermidine at 0.5 mM each. In this stabilized condition, the ribosomes showed maximal incorporation of amino acids into protein. 4. 4. The possible role is discussed of ATP and Mg 2+ as structural intermediaries between RNA and protein in ribosomes.

The chemical structure and stability of yeast ribosomes

The chemical structure and stability of yeast ribosomes

The chemical structure and stability of yeast ribosomes

1. 1. RNAase is associated with yeast ribosomes. The intact ribosomes were stable below 20°, showed no RNAase activity and their ribonucleic acid was resistant to RNAase. However, ribosome-bound RNAase was fully activated and released by incubation at 25°. Ribosomal RNA was denatured and became sensitive to RNAase during incubation at temperatures between 20° and 50°. 2. 2. Adenosine triphosphate was associated with ribosomes. During incubation, conversion of ATP to AMP and liberation of inorganic phosphate from ribosomes were observed. The heat-denaturation of the RNA in ribosomes as measured by hyperchromicity could be reversed by the addition of an ATP-generating system. 3. 3. At 37° the ribosomes were unstable in buffered solution containing 2 mM Mg 2+ but were stabilized by the addition of ATP and spermidine at 0.5 mM each. In this stabilized condition, the ribosomes showed maximal incorporation of amino acids into protein. 4. 4. The possible role is discussed of ATP and Mg 2+ as structural intermediaries between RNA and protein in ribosomes.

Solubilization of labeled protein in cell-free amino acid incorporating systems from rat liver

Experimental evidence has been produced indicating that the solubilization of labeled protein from microsomal ribosomes in cell-free liver systems is not essentially due to unspecific ribosome disintegration. 1. 1. Chromatography of the soluble fraction of the systems on TEAE-cellulose showed that the protein-bound radioactivity was not limited to the nucleoprotein subfractions but exhibited a distribution pattern similar to that obtained in short-term experiments in vivo. 2. 2. The solubilization had a specific demand for potassium, and showed a marked potassium optimum. 3. 3. Conditions which decrease the stability of ribosomes (sub-optimal magnesium concentration, increased ionic strength in the medium) decreased the yield of labeled protein in the soluble fraction. 4. 4. Prolonged incubation caused a loss of labeled protein from the ribosome fraction. This loss was not accompanied by any corresponding increase in the specific activity of the soluble proteins. 5. 5. The solubilization was energy-dependent.

Stability of nuclear ribosomes

The ultracentrifuge pattern of purified ribonucleoprotein particles from isolated calf thymus nuclei has been shown to consist of many components, some of which exhibit aggregation and dissociation reactions that are influenced by divalent cations. The preparation of nuclear ribonucleoprotein particles in an aggregated state is very closely related to, and depends on, the presence of magnesium, and the condition of the extraction medium. Complete removal of magnesium from the ribonucleoprotein causes irreversible dissociation of the particles.