EFFECT OF MAGNESIUM CONCENTRATION IN EXTRACTING MEDIUM ON POLYRIBOSOME CONTENT AND CELL-FREE AMINO ACID INCORPORATING ABILITY OF EXTRACTS OF LOGARITHMIC PHASE CELLS OF A BACILLUS SP

1. This investigation is concerned with the effect of variation in magnesium concentration, at constant monovalent cation concentration, on the distribution of ribosomal components in and on the cell-free amino acid incorporating abilities of extracts of Bacillus amyloliquefaciens disrupted under considerable shear and disrupted gently, with and without depletion of mRNA by actinomycin D in the latter case. 2. Extracts containing mRNA-depleted ribosomes which no longer had the ability to incorporate amino acids into protein contained a small basal level of faster than 70 S sedimenting material. The amount of this material was found to be Mg2+ dependent and is thought to represent aggregates of ribosomes containing no mRNA. 3. Preparations of cells disrupted in the presence of a low Mg2+ concentration. by shear at 2.5 mM Mg2+ or gently with lysozyme at 1.25 mM Mg2+, contained 50-S and 30-S particles which did not associate on increasing the Mg2+ to 10 mM but nevertheless showed considerable ability to incorporate amino acids. 4. The effect of Mg2+ on the polyribosomes in extracts of cells disrupted under mild conditions showed that in the range 5 to 10 mM there was preservation of maximal cell-free amino acid incorporating ability and interconvertibility of ribosomal distribution patterns, below 5 mM Mg2+ both incorporating ability and faster than 70 S sedimenting material was lost. 5. Extracts of cells disrupted by shear under conditions which preserved the maximal cell-free incorporating ability incorporated approximately half as much 14C-labelled amino acid as preparations lysed gently under optimal conditions. 6. When a preparation was isolated in the presence of 5 mM Mg2+ it showed identical kinetics of amino acid incorporation, in the presence of 10 mM Mg2+, to a preparation isolated in 10 mM Mg2+. However, when the incorporation was examined at 5 mM Mg2+ the same preparation incorporated amino acid to only 20% of the 10 mM Mg2+ level. © 1969.