Further observations on the polynucleotide-induced stimulation of protein synthesis by cell-free preparations from rabbit reticulocytes

Speed-accuracy relationships during in vitro and in vivo protein biosynthesis

Poly U-directed incorporation of phenylalanine and leucine into polypeptide has been described in at least 50 papers since 1961. In general, high translation activities are associated with high accuracies, and vice-versa. Moreover, a vast body of independent experimental data (effect of ethanol, temperature, urea, aminoglycosides, etc... on protein synthesis) put together here suggests that, in many circumstances, speed and accuracy of elongation are correlated. This result is to be contrasted with the view that the speed and the fidelity of protein synthesis are two opposing parameters. In this report, recent experimental data on the nature and effect of ribosomal ambiguity (ram) and streptomycin resistance (Strr) mutations are reexamined. Models on the action of streptomycin and other misreading-inducing antibiotics, as well as long-standing ideas on the control of misreading in mammalian systems are critically evaluated. An explanation is provided for the long-befuddling data on the action of gentamicin.

Characterisation of eukaryotic ribosomal proteins

A simple method of two-dimensional polyacrylamide gel electrophoresis is described which affords: (1) high resolution of eukaryotic ribosomal proteins; (2) good recovery of protein in the transfer from first to second dimension; and (3) characterisation of the separated proteins in terms of molecular weights and other electrophoretic properties. Using this method, we have characterised 70 proteins in rabbit reticulocyte ribosomes, 30 from the small subunit and 40 from the large subunit. The molecular weight distribution is compared with those obtained by other authors after fractionation of the proteins in two dimensions.

A study of the thermal stability of ribosomes and biologically active subribosomal particles

1. The ability of Escherichia coli ribosomes to function in poly(U)-directed protein synthesis was measured at elevated temperatures by using thermostable supernatant factors from Bacillus stearothermophilus. The amount of polyphenylalanine synthesized at 55 degrees C was about the same as at 37 degrees C, but the rate of synthesis was increased approximately fivefold. At 60 degrees C the activity of the ribosomes was halved. 2. E. coli ribosomes can sustain the loss of approx. 10% of the double-helical secondary structure of RNA without losing activity. 3. Within the active ribosome the double-helical secondary structure of the rRNA moiety is stabilized compared with isolated rRNA, as judged by enzymic hydrolysis and by measurements of E(260). 4. The main products, over the range 0-55 degrees C, of ribonuclease T(1) digestion of the smaller subribosomal particle of E. coli were two fragments (s(0) (20,w) 15S and 25.3S) of approximately one-quarter and three-quarters of the size of the intact molecule, revealing the presence of a ;weak spot' where intramolecular bonds appear insufficient to hold the fragments together. 5. Subribosomal particles of B. stearothermophilus were more stable to heating, by approx. 10 degrees C, than those of E. coli, and the stabilization of double-helical secondary structure of the RNA moiety was more striking. 6. Rabbit reticulocyte ribosomes were active in poly(U)-directed protein synthesis at 45 degrees C, and half the activity was lost after heating to 53 degrees C. Active subribosomal particles of rabbit reticulocytes and of oocytes of Xenopus laevis, like the bacterial subribosomal particles, underwent a conformational change to a slower-sedimenting form on heating. The temperature range of the transition depended on the species. 7. Slower-sedimenting particles, whether produced by EDTA treatment or by heating, had different ;melting' profiles compared with active subribosomal particles, providing another indication of conformational differences. 8. Comparison of the properties of the various subribosomal particles revealed greater variation in the secondary structure of the protein moieties (judged by measurement of circular dichroism) than in the secondary structure of the RNA moieties, which appeared to have features in common.

Reinitiation of RNA synthesis on transcription of chromatin DNA by Escherichia coli RNA polymerase

The transcription of DNA in chromatin by Escherichia coli RNA polymerase resembles that of isolated DNA in two important respects: the release of nascent RNA and reinitiation of RNA synthesis is dependent on the salt concentration, and RNA synthesis is markedly stimulated by the addition of ribosomes.

The production of biologically active subparticles from rabbit reticulocyte ribosomes

THE EFFECT OF EXPOSING RABBIT RETICULOCYTE RIBOSOMES TO CONCENTRATED SOLUTIONS OF POTASSIUM CHLORIDE WAS EXAMINED BY: (a) dialysis against 0.5m-potassium chloride; (b) zone centrifugation through a sucrose gradient in 0.5m-potassium chloride; (c) differential centrifugation of a solution made 0.5m with respect to potassium chloride. The products of each treatment and their ability to support protein synthesis in a reticulocyte cell-free system, in the presence and in the absence of polyuridylic acid, were examined. The following results were found. (1) Exposing the polysomes to 0.5m-potassium chloride was not a sufficient condition for the complete dissociation of ribosomes into subparticles; the reaction showed a concentration-dependence, implying the existence of an equilibrium between the various ribosomal species. Disturbance of the equilibrium by removing certain products, as in zone centrifuging, can lead to complete dissociation. (2) The subparticles produced by dialysis or sucrose-gradient fractionation were biologically inactive and unstable. (3) The pellet obtained by differential centrifuging consisted of subparticles, if suspended in a Mg(2+)-free buffer; addition of Mg(2+) converted about 30% of the material into heavier sedimenting species, and the preparation had 20-40% of the activity of the untreated control polysomes in the cell-free system. Addition of the 0.5m-potassium chloride supernatant fraction resulted in further apparent reconstitution of sub-particles into ribosomes and polysomes and in a 50-100% restoration of biological activity. When both polyuridylic acid and supernatant factors were present incorporations similar to or higher than those of the control were attained.

Relationship between Protein Synthesis in Tuber Discs and the Protein Synthetic Activity of a Cell-Free Preparation

A cell-free system which synthesizes protein was isolated from ;aged' discs of Jerusalem artichoke tubers. The synthetic activity was largely associated with the fraction containing mitochondria. Preparations from freshly cut tissue were virtually inactive but increasingly active preparations were obtained from discs ;aged' for progressively longer periods; those from 24 hour discs showing maximum activity. The characteristics of this change are reminiscent of the rate of development of invertase, a marker for protein synthesis in the intact disc. Extensive investigations showed that bacterial contamination was not a significant factor in the synthetic activity.