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At least 73 records · Page 4Linked to original sources
PubMed1976

Isotope labeling of free and aminoacyl transfer RNA synthetase-bound transfer RNA.

The structural organization of the complex of Escherichia coli Ile-tRNA synthetase and tRNA Ile has been studied by isotope labeling of purine units in the tRNA. Free or bound tRNA is incubated in tritiated water for 5 to 15 h at 37 degrees in order to incorporate tritium into the C-8 positions of purine units. (Previous work has shown that the labeling rate of a purine is very sensitive to its microenvironment.) Under conditions where exchange-out does not occur, the nucleic acid is digested with nucleases and purines are subsequently isolated from known locations in the structure. Four purines are substantially perturbed by bound Ile-tRNA synthetase; in each case, the rate of labeling is retarded in the presence of the synthetase. The four purines occur at or near the 3' terminus and at the interface of the dihydrouridine stem and loop. These bases occur in segments of the tRNA that previous photochemical cross-linking studies have identified as important for synthetase-tRNA interactions. It appears that the effects observed on these sites are caused by their direct interaction with or shielding by the bound synthetase. In addition, two other sites, one in the anticodon and one in the amino acid acceptor-T psi C helix, appear to be perturbed (retarded labeling rates) by the bound enzyme. The data also suggest there is no significant conformational change in the tRNA upon binding to the synthetase.

Adenine Nucleotides↗
PubMed1979

Regulation of biosynthesis of aminoacyl-transfer RNA synthetases and of transfer-RNA in Escherichia coli.

We have isolated temperature resistant revertants from temperature sensitive E. coli strains containing either a thermolabile glutaminyl-tRNA synthetase or leucyl-tRNA synthetase. Among the revertants which still contained the thermolabile leucyl-tRNA synthetase we found two classes of regulatory mutants (leuX and leu Y) which have elevated levels of this enzyme. The leuX mutation specifies an operator-promoter region adjacent to the structural gene (leuS) for the enzyme. The leuY gene maps away from the leuS gene and codes for a protein. Using these mutants we demonstrated that the levels of leucyl-tRNA are related to the derepression of the leucine and isoleucine-valine operons. Among the revertants which still contained the thermolabile glutaminyl-tRNA synthetase were characterized three classes of mutants, glnT, glnU, and glnR. The glnT and glnU mutants contain elevated levels of tRNAgln, while the glnR mutant possesses elevated levels of glutaminyl-tRNA synthetase. The level of glutamine synthetase, the enzyme responsible for the formation of glutamine, is also derepressed in the glnT and glnR mutants.

Amino Acyl-tRNA Synthetases↗
PubMed1994

The importance of conserved nucleotides of 23 S ribosomal RNA and transfer RNA in ribosome catalyzed peptide bond formation.

We have constructed the double mutant G2252C/G2253C in Escherichia coli 23 S rRNA by site-directed mutagenesis. These phylogenetically conserved residues are protected from chemical modification by the 3' CCA terminus of the peptidyl-tRNA site (P site)-bound tRNA. Expression of C2252/C2253 23 S rRNA in E. coli severely compromises cell growth. Mutant rRNA is assembled into 50 S subunits and 70 S ribosomes but is discriminated against in polysomes. Mutant ribosomes function at lower rates in peptidyltransferase assays than wild type ribosomes. To test whether this defect derives from disruption of base pairing with the 2 cytidines of the invariant 3' CCA terminus of tRNA, a mutant E. coli tRNAPhe gene was constructed, with the CCA sequence changed to GGA. As deacylated species, mutant and wild type tRNAPhe inhibit peptidyl transfer identically. Mutant tRNAPhe was aminoacylated in vitro but failed to react as a P site substrate, with either mutant or wild type ribosomes. These results support a role for G2252 and G2253 of 23 S rRNA in peptidyltransferase function and a role for the 3' residues of peptidyl-tRNA in catalytically productive P site interaction; but they fail to provide evidence supporting canonical base pairing between these 23 S residues and the 3' end of peptidyl-tRNA.

Base Sequence↗
PubMed1966

Cytokinin activity: localization in transfer RNA preparations.

Transfer RNA from yeast, liver, and Escherichia coli has cytokinin activity in the tobacco callus bioassay, whereas ribosomal RNA from yeast is inactive. In contrast to fractions of yeast transfer RNA rich in serine acceptor and cytokinin activity, preparations (70 to 90 percent pure) of arginine transfer RNA(2), glycine transfer RNA, phenylalanine transfer RNA, and valine transfer RNA(1) and of highly purified alanine transfer RNA from yeast were inactive at concentrations of 20 to 2500 micrograms per liter. One molecule of 6-(gamma,gamma-dimethylallylamino) purine per 20 molecules of yeast tRNA would account for the observed cytokinin activity. The number of major molecular species contributing to cytokinin activity of transfer RNA, therefore, must be small.

Chromatography↗
PubMed1973

Biosynthesis of transfer RNA: in vitro conversion of transfer RNA precursors from Bombyx mori to 4S RNA by Escherichia coli enzymes.

Evidence for the presence of rapidly labeled short-lived RNA species, presumed to be precursors to transfer RNA (tRNA), in the silk glands of Bombyx mori is presented. These precursors, which migrate between 4S and 5S markers on acrylamide gels, can be converted in vitro into molecules indistinguishable in size from tRNA. The conversion is also catalyzed by a crude enzyme fraction isolated from ribosomes of E. coli. Since a similar enzyme preparation cleaves the suppressor tRNA(Tyr) sequence of E. coli from its precursor molecule, it would appear that the precursor to E. coli tRNA(Tyr) and the precursors to silk-gland tRNAs share common structural features.

Animals↗
PubMed1983

Codon-induced transfer RNA association. A property of transfer RNA involved in its adaptor function?

It is shown by equilibrium sedimentation that the binding of cognate codons to tRNAPhe (yeast), tRNAPhe (Escherichia coli), tRNALys, tRNAfMet and of the wobble codon UUU to tRNAPhe (yeast) induces dimerization of codon transfer RNA complexes. Analysis of the sedimentation profiles with a quantitative evaluation of the coupling between sedimentation and association equilibrium provides dimerization constants in the range from 1 X 10(4) to 6 X 10(4) M-1. These results on various tRNAs from different organisms suggest that the codon-induced tRNA association is a general phenomenon. Probably the codon-induced tRNA association facilitates the aminoacyl transfer reaction.

Codon↗
PubMed1991

An Escherichia coli tyrosine transfer RNA is a leucine-specific transfer RNA in the yeast Saccharomyces cerevisiae.

While the Escherichia coli Su-3 (tyrT) tyrosine tRNA suppressor inserts only tyrosine at amber codons in E. coli, we show here that in Saccharomyces cerevisiae this tRNA inserts leucine and no significant amounts of any other amino acid. Thus, the E. coli tyrosine tRNA is functionally a leucine tRNA in yeast cytoplasm. This functional identity may correlate with a structural relationship between the E. coli tyrosine and yeast leucine tRNAs, which are both members of the uncommon type II class of tRNA structures. The results raise the possibility that in evolution a tRNA may be more closely related to a tRNA of different acceptor specificity, but of the same type class, than to one with the same amino acid specificity, but of a different type class.

Alleles↗
PubMed1977

Kinetin incorporated into tobacco callus ribosomal RNA and transfer RNA preparations.

Kinetin, N(6)-furfuryladenine, was incorporated into tobacco (nicotiana tabacum L., var. Wis. No. 38) callus RNA isolated from rapidly growing tissue cultured in the presence of N(6)-furfuryladenine-8-(14)C or unlabeled kinetin. Approximately 0.7% of the radioactivity in the labeled kinetin added to the medium was recovered as N(6)-furfuryladenosine (fr(6)A) in the rRNA and tRNA preparations from the tobacco callus. The rRNA contained over 90% of these fr(6) A moieties. The extent of kinetin incorporation was four times greater than that observed for N(6)-benzyladenine. The radiochemical purity of the recovered fr(6) A was confirmed by three successive chromatographic purifications on Sephadex columns (LH-20 eluted with 35% ethanol, G-10 eluted with 20% ethanol, and LH-20 eluted with water). A cytokinin-active ribonucleoside with elution volumes corresponding to fr(6) A was isolated from the tobacco callus rRNA preparation. This compound was analyzed by gas-liquid chromatography and rigorously characterized as N(6)-furfuryladenosine by gas-liquid chromatography-mass spectrometry of the trimethylsilyl derivative.

Journal Article↗