Effect of trypsin on Escherichia coli and rabbit reticulocyte ribosomes

Tetracyclines induce changes in accessibility of ribosomal proteins to proteases

Limited proteolysis was used to test the interaction of tetracyclines and some of their derivatives with ribosomes. Proteolysis of the free ribosomes was compared with that of the ligand-bound ribosomes. The interaction of different tetracyclines with ribosomes depends on their chemical structure and produces both a protective effect and an increased susceptibility to proteases of some ribosomal proteins in the 30S and 50S subparticles. Most of the proteins affected by tetracycline action are located on the head of the 30S and interface side of the 50S subunits. On the grounds of the obtained data one of the antibiotic-binding regions can be located near the ribosomal peptidyl transferase center. The effect of possible conformational changes induced by tetracyclines on the translation process is discussed.

The L7/L12 proteins change their conformation upon interaction of EF-G with ribosomes

The different functional complexes of ribosomes with elongation factor F (EF-G) were studied by digestion experiments with trypsin. It was found that upon interaction of EF-G with ribosomes the L7/L12 proteins are sensitive to trypsin and are trypsin resistant after dissociation of EF-G from ribosomes. The significance of conformational alterations in the L7/L12 and also in the other proteins in the translation process is discussed.

Effect of sulfhydryl reagents on the ribosomes of Bacillus subtilis

The effect of various sulfhydryl reagents on the ribosomes of Bacillus subtilis was studied. The 70S ribosomes were completely dissociated into 30S and 50S subunits by appropriate concentrations of p-chloromercuribenzoic acid (PCMB) and 5,5'-dithio-bis-(2-nitro-benzoic acid). The N-ethylmaleimide and iodoacetamide failed to dissociate the ribosomes even at relatively high concentrations. The rate of dissociation of ribosomes by PCMB varied with the concentration of ribosomes. A progressive decrease in the rate of dissociation was observed as the concentration of ribosomes in the reaction mixture was increased. The PCMB-induced ribosomal subunits were unable to reassociate into 70S monomers unless they were dialyzed against buffer containing beta-mercaptoethanol. On the average, four molecules of PCMB per 70S ribosome and two molecules of PCMB per each 30S and 50S subunit were bound. The number of PCMB molecules bound per ribosome did not change with increasing concentrations of PCMB, even though higher concentrations of PCMB resulted in dissociation of ribosomes into subunits.

Differences in the ribosomes prepared from lactating and non-lactating bovine mammary gland

1. Ribosomes prepared from bovine lactating mammary gland are able to synthesize protein, whereas similar preparations from non-lactating glands are not. Washing the ribosome suspensions through a medium containing 0.5m-ammonium chloride enhanced their ability to incorporate phenylalanine into polyphenylalanine. 2. Ribosomes isolated from non-lactating bovine mammary gland, in contrast with those from rat liver and lactating mammary gland, contained significant amounts of extraneous nucleases. These enzymes could be removed by washing with a medium A buffer containing 0.5m-ammonium chloride. 3. Only those ribosomes from functionally active tissues were able to bind polyuridylic acid and phenylalanyl-tRNA.

Ribonuclease activity in commercial crystalline trypsin and a method for removal

Several preparations of crystalline trypsin hydrolyze RNA because of contaminating ribonuclease activity. Filtration of these materials through Sephadex G-50 yields a trypsin devoid of ribonuclease activity and having a proteolytic specific activity about 70 percent of the starting material.

The relation of RNA and protein synthesis to the sedimentation of muscle ribosomes: effect of diabetes and insulin

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