Extensive charging of transfer ribonucleic acid by bean leaf extracts in vitro

1. Phenol was effectively removed from aqueous extracts of RNA by chromatography on Sephadex G-50. 2. Elution of tRNA from Sephadex G-50 columns at pH7.6 was shown to remove 91% of the endogenously bound amino acids. 3. tRNA prepared without recourse to ethanolic precipitation was capable of accepting much greater amounts of amino acids than could redissolved samples of precipitated tRNA. 4. Aminoacyl-tRNA synthetase enzymes were partially purified with calcium phosphate gel. Elution of enzymes from the gel at pH6.5 yielded a fraction having phenylalanine- and alanine-charging activity, but no aspartate-, lysine- or proline-charging activity, whereas elution at pH7.6 gave a fraction having aspartate-, lysine- and proline-charging activity but no phenylalanine- or alanine-charging activity. 5. By using partially synthetase enzymes and tRNA eluted from DEAE-Sephadex A-50 columns, 52% of the theoretical maximum of aminoacyl-tRNA synthesis was obtained in vitro.

Effect of 4-azaleucine upon leucine metabolism in Salmonella typhimurium

dl-4-Azaleucine (5 x 3(-3)m) added to exponentially growing cells of Salmonella typhimurium resulted in an abrupt cessation of growth lasting 4 to 8 hr followed by a resumption of division. The transitory nature of inhibition was not due to the instability or modification of the analogue or to a derepression of leucine-forming enzymes. Of many compounds tested, leucine served most efficiently to reverse 4-azaleucine-induced inhibition. Inhibition of growth can be explained by the fact that 4-azaleucine inhibits alpha-isopropylmalate synthase, the first enzyme unique to leucine biosynthesis. The analogue was a poor inhibitor of both the transamination of alpha-ketoisocaproate to leucine and the charging of leucine to transfer ribonucleic acid. With a leucine auxotroph starved for leucine, the analogue was incorporated into protein specifically in place of leucine. Such incorporation was accompanied by the death of almost all of the cells.

Regulation of tyrosyl-transfer ribonucleic acid synthetase in Bacillus subtilis

Derepression of tyrosyl-transfer ribonucleic acid synthetase in Bacillus subtilis was observed in strains grown with limiting tyrosine, but not in regulatory mutants derepressed in biosynthetic enzyme synthesis.

Factors controlling aminoacyl-transfer-ribonucleic acid synthesis in vitro by a plant system

1. Factors affecting aminoacyl-tRNA synthesis in vitro by cell-free preparations from bean leaves were investigated. 2. Evidence was obtained that optimum concentrations as well as correct ratios of Mg(2+) and ATP are required for aminoacyl-tRNA synthesis in the bean-leaf system. 3. The results indicated that pH is a controlling factor having differential effects on the formation of individual aminoacyl-tRNA species. The possible micro-regulatory function of pH in protein synthesis in vivo is discussed with special reference to alanyl-tRNA formation. 4. Very low rates of alanine-stimulated pyrophosphate exchange were observed in the absence of tRNA. This observation is discussed relative to proposals about the mechanism of aminoacyl-tRNA synthesis.