Effect of alanine, leucine and fructose on lysyl-transfer ribonucleic acid ligase activity in a mutant of Escherichia coli K-12

A mutant of Escherichia coli K-12 was examined which has growth medium-dependent lysyl-transfer ribonucleic acid (tRNA) ligase activity. In minimal medium or 0.5% yeast extract, the activity of the enzyme in the mutant strain was 5 to 10% of wild type. However, when the mutant was grown in a highly enriched medium, such as AC broth (Difco), the activity of the mutant ligase increased 10- to 20-fold. We found that the supplementation of 0.5% yeast extract by l-alanine plus d-fructose replaces the need for the highly enriched medium. Fructose plus l-leucine and fructose plus l-alpha-amino-n-butyric acid were also stimulatory, but not as effective as fructose and alanine. With minimal medium, a combination of carbohydrate (fructose or glucose) plus alanine and leucine was required to replace the enriched medium. The most effective combination was fructose, glucose, alanine, and leucine. Lysyl-tRNA ligase was stimulated 1.5 to 2-fold in the wild-type strain or Hfr H (Hayes) by fructose plus alanine when these strains were cultured in 0.5% yeast extract. Experiments employing the combined technique of density labeling with D(2)O and isopycnic centrifugation in cesium chloride indicated that the increased activity of lysyl-tRNA ligase observed in AC broth or in the presence of fructose, glucose, alanine, and leucine is due to the synthesis of new enzyme.

Activity of sRNA amino acyl synthetases in ontogenic development of rabbit brain

The purpose of the study was the estimation of the changes in the activity of 20 individual sRNA amino acyl synthetases in the newborn, 12th, 30th, 48th and 180th days old rabbit brain. The investigations showed that the highest enzyme activity was found in the pH 5 fraction obtained from the CNS of newborn rabbits. In the further period of brain’s development there was a decline in the activity of amino acyl sRNA synthetases beginning from the 12th day of extrauterine life and continuing until the animals were 48 days old, when the activity approximated that measured in the adult rabbit brain. The activity of these enzymes in the developing brain was higher in the cerebral cortex than in the white matter.

Protein synthesis by the psychophiles Bacillus psychophilus and Bacillus insolitus

Protein synthesis by whole cells of two psychrophilic bacteria, Bacillus psychrophilus and Bacillus insolitus, directly corresponded to the growth of these organisms at 5, 20 and 30C, with a smaller total amount of growth and protein synthesis occurring at 30C than at 20C. When the effect of temperature on protein synthesis was examined using extracts, the capability to carry out poly U directed incorporation of 14C-L-phenylalanine into protein was inhibited by 30C as compared to 5C. The temperature sensitivity of the cell-free protein synthesizing systems was not due to the presence of heat-sensitive aminoacyl-tRNA synthetases. Investigation of the effect of separately heating at 30C washed ribosome (W-RIB) and supernatant (IS-100) fractions prepared from these microorganisms, followed by recombination and reaction at 15C, showed that the temperature sensitivity of the protein synthesis resided in the ribosomal fraction of the cells

Hydrocortisone induction of rat-liver leucyl-transfer RNA and its synthetases

Within 3 hr after the intraperitoneal administration of hydrocortisone to female rats, a new leucine-accepting tRNA and a new leucyl-tRNA synthetase activity appear in the liver cytosol. The new isoaccepting tRNA can be acylated only with the synthetase derived from livers of hormone-treated animals. Both components are transient; by 12 hr after hydrocortisone administration, the isoaccepting tRNA and its synthetase disappear from livers of treated animals.

Different arginine transfer ribonucleic acid species prevalent in shaken and unshaken cultures of Neurospora

When the arginyl-transfer ribonucleic acid (tRNA) species isolated from unshaken and from shaken cultures of Neurospora were compared by co-chromatography, a marked change in the relative abundance of the two main tRNA(arg) species was found. The two arginine tRNA species had different codon responses in ribosome binding assays. The tRNA(arg) eluting first (prevalent in shaken cultures) bound strongly to polyadenylic-guanylic acid [poly(A,G)] and to a lesser extent to polycytidylic-guanylic-adenylic acid [poly(C,G,A)]. The second tRNA(arg) species (prevalent in unshaken cultures) bound to poly(C,G,A) but not to poly(A, G). The possible significance of these observations is briefly discussed. Several modifications that improve the yield of tRNA from Neurospora were introduced in a standard isolation procedure.

Regulation of the tyrosine biosynthetic enzymes in Salmonella typhimurium: analysis of the involvement of tyrosyl-transfer ribonucleic acid and tyrosyl-transfer ribonucleic acid synthetase

Mutants of Salmonella typhimurium were isolated that require tyrosine for growth because of an altered tyrosyl-transfer ribonucleic acid (tRNA) synthetase. Extracts of one strain (JK10) contain a labile enzyme with decreased ability to transfer tyrosine to tRNA(Tyr) and a higher K(m) for tyrosine than the wild-type enzyme. Strain JK10 maintains repressed levels of the tyrosine biosynthetic enzymes when the growth rate is restricted due to limitation of charged tRNA(Tyr). Several second-site revertants of strain JK10 exhibit temperature-sensitive growth due to partially repaired, heat-labile tyrosyl-tRNA synthetase. The tyrosine biosynthetic enzymes are not derepressed in thermosensitive strains grown at the restrictive temperature. A class of tyrosine regulatory mutants, designated tyrR, contains normal levels of tyrosyl-tRNA synthetase and tRNA(Tyr). These results suggest that charging of tRNA(Tyr) is not necessary for repression. This conclusion is substantiated by the finding that 4-aminophenylalanine, a tyrosine analogue which causes repression of the tyrosine biosynthetic enzymes, is not attached to tRNA(Tyr) in vivo, nor does it inhibit the attachment reaction in vitro. A combined regulatory effect due to the simultaneous presence of tyrS and tyrR mutations in the same strain was detected. The possibility of direct participation of tyrosyl-tRNA synthetase in tyrosine regulation is discussed.