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PubMed2006

Crystallization and preliminary X-ray analysis of the tRNA thiolation enzyme MnmA from Escherichia coli complexed with tRNA(Glu).

MnmA catalyzes a sulfuration reaction to synthesize 2-thiouridine at the wobble positions of tRNA(Glu), tRNA(Gln) and tRNA(Lys) in Escherichia coli. The binary complex of MnmA and tRNA(Glu) was crystallized in two different crystal forms: forms I and II. Cocrystallization of MnmA-tRNA(Glu) with ATP yielded form III crystals. The three crystal forms diffracted to 3.1, 3.4 and 3.4 angstroms resolution, respectively, using synchrotron radiation at SPring-8. These crystals belong to space groups C2, I2(1)2(1)2(1) and C2, with unit-cell parameters a = 225.4, b = 175.8, c = 53.0 angstroms, beta = 101.6 degrees, a = 101.5, b = 108.0, c = 211.2 A and a = 238.1, b = 102.1, c = 108.2 angstroms, beta = 117.0 degrees, respectively. The asymmetric units of these crystals are expected to contain two, one and two MnmA-tRNA(Glu) complexes, respectively.

Cloning, Molecular↗
PubMed2004

A proline tRNA(CGG) gene encompassing the attachment site of temperate phage 16-3 is functional and convertible to suppressor tRNA.

Several temperate bacteriophage utilize chromosomal sequences encoding putative tRNA genes for phage attachment. However, whether these sequences belong to genes which are functional as tRNA is generally not known. In this article, we demonstrate that the attachment site of temperate phage 16-3 (attB) nests within an active proline tRNA gene in Rhizobium meliloti 41. A loss-of-function mutation in this tRNA gene leads to significant delay in switching from lag to exponential growth phase. We converted the putative Rhizobium gene to an active amber suppressor gene which suppressed amber mutant alleles of genes of 16-3 phage and of Escherichia coli origin in R. meliloti 41 and in Agrobacterium tumefaciens GV2260. Upon lysogenization of R. meliloti by phage 16-3, the proline tRNA gene retained its structural and functional integrity. Aspects of the co-evolution of a temperate phage and its bacterium host is discussed. The side product of this work, i.e. construction of amber suppressor tRNA genes in Rhizobium and Agrobacterium, for the first time widens the options of genetic study.

Agrobacterium tumefaciens↗
PubMed1982

The properties of the tRNA . protein complex of the Escherichia coli ribosome. Interaction with tRNA, 5-S RNA and 30-S ribosomal subunit.

A complex between immobilized tRNA and Escherichia coli 50-S ribosomal subunit proteins provides binding sites for several other components of the protein biosynthesis system. We found that this complex binds 5-S RNA. tRNA and 30-S ribosomal subunits. The binding of 5-S RNA and tRNA takes place at equilibrium; in 10 mM Tris/HCl buffer pH 7.5, containing 10 mM MgCl2 and 100 mM KCl at 4 degrees C it is characterized by the dissociation constants 1.7 X 10(-7) M and 4 X 10(-7) M respectively. We show that the performed complex between tRNA and 50-S ribosomal subunit protein can bind these two RNAs simultaneously by forming a subribosomal domain consisting of two molecules of tRNA, 5-S RNA and the ribosomal proteins L2, L15, L16, L17, L18, L22, L33 and L34. The preformed tRNA . protein complex interacts also with the 30-S ribosomal subunit, suggesting that is located at the ribosomal interface.

Escherichia coli↗
PubMed1995

Modulation of tRNA(iMet), eIF-2, and eIF-2B expression shows that GCN4 translation is inversely coupled to the level of eIF-2.GTP.Met-tRNA(iMet) ternary complexes.

To understand how phosphorylation of eukaryotic translation initiation factor (eIF)-2 alpha in Saccharomyces cerevisiae stimulates GCN4 mRNA translation while at the same time inhibiting general translation initiation, we examined the effects of altering the gene dosage of initiator tRNA(Met), eIF-2, and the guanine nucleotide exchange factor for eIF-2, eIF-2B. Overexpression of all three subunits of eIF-2 or all five subunits of eIF-2B suppressed the effects of eIF-2 alpha hyperphosphorylation on both GCN4-specific and general translation initiation. Consistent with eIF-2 functioning in translation as part of a ternary complex composed of eIF-2, GTP, and Met-tRNA(iMet), reduced gene dosage of initiator tRNA(Met) mimicked phosphorylation of eIF-2 alpha and stimulated GCN4 translation. In addition, overexpression of a combination of eIF-2 and tRNA(iMet) suppressed the growth-inhibitory effects of eIF-2 hyperphosphorylation more effectively than an increase in the level of either component of the ternary complex alone. These results provide in vivo evidence that phosphorylation of eIF-2 alpha reduces the activities of both eIF-2 and eIF-2B and that the eIF-2.GTP. Met-tRNA(iMet) ternary complex is the principal component limiting translation in cells when eIF-2 alpha is phosphorylated on serine 51. Analysis of eIF-2 alpha phosphorylation in the eIF-2-overexpressing strain also provides in vivo evidence that phosphorylated eIF-2 acts as a competitive inhibitor of eIF-2B rather than forming an excessively stable inactive complex. Finally, our results demonstrate that the concentration of eIF-2-GTP. Met-tRNA(iMet) ternary complexes is the cardinal parameter determining the site of reinitiation on GCN4 mRNA and support the idea that reinitiation at GCN4 is inversely related to the concentration of ternary complexes in the cell.

Binding, Competitive↗
PubMed1999

Hormonal induction of mouse selenocysteine transfer ribonucleic acid (tRNA) gene transcription-activating factor and its functional importance in the selenocysteine tRNA gene transcription in mouse mammary gland.

Mouse selenocysteine transfer RNA (tRNA) gene transcription-activating factor (mStaf) is a transcriptional activator that enhances RNA polymerase III-dependent mouse selenocysteine tRNA (tRNA(Sec)) gene transcription. The DNA-binding activity of mStaf in mouse mammary gland undergoes developmental changes, reaching a maximal level during the period of lactation. In this study, we employed an organ culture system to examine the hormonal regulation of mStaf binding and its role in the tRNA(Sec) transcription in the mammary gland. The results showed that mStaf binding in mammary explants was stimulated by treatment with the lactogenic hormones, PRL, insulin, and hydrocortisone and that a specific MEK inhibitor, PD98059, inhibited the hormonal stimulation of mStaf binding. Other kinase inhibitors, such as a Janus kinase inhibitor and a calmodulin kinase inhibitor, had no apparent effect. Northern and Western blot analyses revealed that the level of both mStaf messenger RNA and protein was enhanced by the lactogenic hormones and was reduced by the concomitant treatment with PD98059. The mitogen-activated protein kinase activity in cultured explants was rapidly induced and maintained at high levels by the lactogenic hormones. We also found that the lactogenic hormones increased the amount of tRNA(Sec) in a time-dependent manner, which followed the increase in mStaf binding in cultured mammary explants. These results support the view that mStaf plays a key role in the hormonal stimulation of tRNA(Sec) transcription in the mammary gland.

Animals↗
PubMed2006

tRNA regulation of gene expression: interactions of an mRNA 5'-UTR with a regulatory tRNA.

Many genes encoding aminoacyl-tRNA synthetases and other amino acid-related products in Gram-positive bacteria, including important pathogens, are regulated through interaction of unacylated tRNA with the 5'-untranslated region (5'-UTR) of the mRNA. Each gene regulated by this mechanism responds specifically to the cognate tRNA, and specificity is determined by pairing of the anticodon of the tRNA with a codon sequence in the "Specifier Loop" of the 5'-UTR. For the 5'-UTR to function in gene regulation, the mRNA folding interactions must be sufficiently stable to present the codon sequence for productive binding to the anticodon of the matching tRNA. A model bimolecular system was developed in which the interaction between two half molecules ("Common" and "Specifier") would reconstitute the Specifier Loop region of the 5'-UTR of the Bacillus subtilis glyQS gene, encoding GlyRS mRNA. Gel mobility shift analysis and fluorescence spectroscopy yielded experimental Kds of 27.6 +/- 1.0 microM and 10.5 +/- 0.7 microM, respectively, for complex formation between Common and Specifier half molecules. The reconstituted 5'-UTR of the glyQS mRNA bound the anticodon stem and loop of tRNA(Gly) (ASL(Gly)(GCC)) specifically and with a significant affinity (Kd = 20.2 +/- 1.4 microM). Thus, the bimolecular 5'-UTR and ASL(Gly)(GCC) models mimic the RNA-RNA interaction required for T box gene regulation in vivo.

5' Untranslated Regions↗
PubMedDate not supplied

[Escherichia coli ribosomes having peptidyl-tRNA and deacylated tRNA at the A- and P-sites, respectively, may not be competent in translocation].

Ribosomes can have two states at 0 degree C: competent and noncompetent in translocation. In both states poly(U)-programmed ribosomes bind phenylalanyl-tRNA to A and P sites and form peptide bond. Elongation factor G promotes fast translocation in competent ribosomes and makes them noncompetent ones. Initial correlation between competent and noncompetent ribosomes is 2:1. Addition of deacylated tRNA does not influence phenomenon described as well as thermal reactivation of the ribosomes before beginning of the experiments. The possibility of deacylated tRNA translocation is shown. The translocation does not occurred provided that at least one of the ribosome sites is filled with shortened tRNA analog (tRNA with truncated CCA-end or tRNA anticodon arm).

Acylation↗
PubMed1990

Recognition of the tRNA-like structure in tobacco mosaic viral RNA by ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli and Saccharomyces cerevisiae.

The 3'-terminal tRNA-like structure of the tobacco mosaic virus RNA interacts with ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli or yeast in much the same manner as do tRNAs. Primary sites of interaction cluster near the 3' end and in the loop proposed to be analogous to the psi-loop of a tRNA. Some modified bases in the tRNA-like structure inhibit interaction with nucleotidyltransferase, yet the analogous bases in a tRNA do not. The location of some of these nucleotides within the analog to the psi-loop suggests that this structure differs slightly from its counterpart in a tRNA. The location of other such bases in the helical stem near the 3' end can be explained if the pseudoknot is disrupted by these modified bases or if the tertiary structure of the RNA is altered in the enzyme-RNA complex. A partially denatured secondary structure that persists on denaturing gels is proposed.

Base Sequence↗
PubMed1979

Sequence analysis of two yeast mitochondrial DNA fragments containing the genes for tRNA Ser UCR and tRNA Phe UUY.

Two restriction enzyme fragments containing yeast mitochondrial tRNA genes have been characterized by DNA sequence analysis. One of these fragments is 320 base pairs long and contains a tRNA Ser gene. The corresponding tRNA SER was isolated from yeast mitochondria and its nucleotide sequence also was determined. This mitochondrial tRNA is 90 nucleotides in length, has a G + C content of 38%, and has UGA as the anticodon. A portion of a 680-base-pair DNA fragment containing a tRNA Phe gene was also sequenced. The portion of this gene which codes for the mature tRNA is 75 base pairs in length, has a G + C content of 33%, and contains the anticodon GAA. Neither gene contains an intervening sequence or codes for the 3' CCA terminus. Both are surrounded by regions of more than 90% A + T. The significance of these sequences is discussed.

Base Sequence↗
PubMedDate not supplied

[Poly(U)-dependent interaction of yeast tRNA(Phe) and its fragments with Escherichia coli ribosomes. II. Localization of tRNA binding centers with a P-site].

Poli(U)-dependent binding of yeast tRNA(Phe) lacking the 3'-terminal CA or CCA residues, and fragments of tRNA prepared by splitting the tRNA(Phe) at the G18 or 7mG46 nucleotides, to the 70S ribosomal P-site was studied. Equilibrium binding constants and free energies of binding were measured. The contribution of C74 and C75 was estimated at 3.9 kJ/mol and 3.0 kJ/mol, respectively, at 10 mM Mg2+ and 30 degrees C. The free energies of the binding of the anticodon arm the tRNA lacking its CCA terminus, and the tRNA fragment containing bases N1-N45 were found to be nearly equal. These results indicate that only the anticodon arm and the CCA terminus take part in deacylated tRNA-P-site interaction.

Anticodon↗
PubMed1984

Modification of specific lysine residues in E. coli methionyl-tRNA synthetase by crosslinking to E. coli formylmethionine tRNA.

A protein affinity labeling derivative of E. coli tRNAfMet has been prepared which carries an average of one reactive side chain per molecule, distributed over four structural regions. Each side chain contains a disulfide bond capable of reaction with cysteine residues and an N-hydroxysuccinimide ester group capable of coupling to lysine epsilon-amino groups in proteins. Reaction of the modified tRNA with E. coli methionyl-tRNA synthetase leads to crosslinking only by reaction with lysine residues in the protein. Examination of the tRNA present in the crosslinked complex reveals that the enzyme is coupled to side chains attached to the 5' terminal nucleotide, the dihydrouridine loop, the anticodon and the CCA sequence. Digestion of the crosslinked enzyme with trypsin followed by peptide mapping reveals that the major crosslinking reactions occur at four specific lysine residues, with minor reaction at two additional sites. Native methionyl-tRNA synthetase contains 90 lysine residues, 45 in unique sequences of the dimeric alpha 2 enzyme. Crosslinking of the protein to different regions in tRNAfMet thus occurs with the high degree of selectivity necessary for use in determining the peptide sequences which are near specific nucleotide sequences of tRNA bound to the protein.

Amino Acyl-tRNA Synthetases↗
PubMed1995

Tryptophanyl-tRNA synthetase crystal structure reveals an unexpected homology to tyrosyl-tRNA synthetase.

BACKGROUND: Tryptophanyl-tRNA synthetase (TrpRS) catalyzes activation of tryptophan by ATP and transfer to tRNA(Trp), ensuring translation of the genetic code for tryptophan. Interest focuses on mechanisms for specific recognition of both amino acid and tRNA substrates. RESULTS: Maximum-entropy methods enabled us to solve the TrpRS structure. Its three parts, a canonical dinucleotide-binding fold, a dimer interface, and a helical domain, have enough structural homology to tyrosyl-tRNA synthetase (TyrRS) that the two enzymes can be described as conformational isomers. Structure-based sequence alignment shows statistically significant genetic homology. Structural elements interacting with the activated amino acid, tryptophanyl-5'AMP, are almost exactly as seen in the TyrRS:tyrosyl-5'AMP complex. Unexpectedly, side chains that recognize indole are also highly conserved, and require reorientation of a 'specificity-determining' helix containing a conserved aspartate to assure selection of tryptophan versus tyrosine. The carboxy terminus, which is disordered and therefore not seen in TyrRS, forms part of the dimer interface in TrpRS. CONCLUSIONS: For the first time, the Bayesian statistical paradigm of entropy maximization and likelihood scoring has played a critical role in an X-ray structure solution. Sequence relatedness of structurally superimposable residues throughout TrpRS and TyrRS implies that they diverged more recently than most aminoacyl-tRNA synthetases. Subtle, tertiary structure changes are crucial for specific recognition of the two different amino acids. The conformational isomerism suggests that movement of the KMSKS loop, known to occur in the TyrRS transition state for amino acid activation, may provide a basis for conformational coupling during catalysis.

Amino Acid Sequence↗
PubMed1987

Covalent coupling of 4-thiouridine in the initiator methionine tRNA to specific lysine residues in Escherichia coli methionyl-tRNA synthetase.

A new method has been developed to couple a lysine-reactive cross-linker to the 4-thiouridine residue at position 8 in the primary structure of the Escherichia coli initiator methionine tRNA (tRNAfMet). Incubation of the affinity-labeling tRNAfMet derivative with E. coli methionyl-tRNA synthetase (MetRS) yielded a covalent complex of the protein and nucleic acid and resulted in loss of amino acid acceptor activity of the enzyme. A stoichiometric relationship (1:1) was observed between the amount of cross-linked tRNA and the amount of enzyme inactivated. Cross-linking was effectively inhibited by unmodified tRNAfMet, but not by noncognate tRNAPhe. The covalent complex was digested with trypsin, and the resulting tRNA-bound peptides were purified from excess free peptides by anion-exchange chromatography. The tRNA was then degraded with T1 ribonuclease, and the peptides bound to the 4-thiouridine-containing dinucleotide were purified by high-pressure liquid chromatography. Two major peptide products were isolated plus several minor peptides. N-Terminal sequencing of the peptides obtained in highest yield revealed that the 4-thiouridine was cross-linked to lysine residues 402 and 439 in the primary sequence of MetRS. Since many prokaryotic tRNAs contain 4-thiouridine, the procedures described here should prove useful for identification of peptide sequences near this modified base when a variety of tRNAs are bound to specific proteins.

Amino Acyl-tRNA Synthetases↗
PubMed1990

Identification of the tRNA anticodon recognition site of Escherichia coli methionyl-tRNA synthetase.

We have previously shown that the anticodon of methionine tRNAs contains most, if not all, of the nucleotides required for specific recognition of tRNA substrates by Escherichia coli methionyl-tRNA synthetase [Schulman, L. H., & Pelka, H. (1988) Science 242, 765-768]. Previous cross-linking experiments have also identified a site in the synthetase that lies within 14 A of the anticodon binding domain [Leon, O., & Schulman, L. H. (1987) Biochemistry 26, 5416-5422]. In the present work, we have carried out site-directed mutagenesis of this domain, creating conservative amino acid changes at residues that contain side chains having potential hydrogen-bond donors or acceptors. Only one of these changes, converting Trp461----Phe, had a significant effect on aminoacylation. The mutant enzyme showed an approximately 60-100-fold increase in Km for methionine tRNAs, with little or no change in the Km for methionine or ATP or in the maximal velocity of the aminoacylation reaction. Conversion of the adjacent Pro460 to Leu resulted in a smaller increase in Km for tRNA(Mets), with no change in the other kinetic parameters. Examination of the interaction of the mutant enzymes with a series of tRNA(Met) derivatives containing base substitutions in the anticodon revealed sequence-specific interactions between the Phe461 mutant and different anticodons. Km values were highest for tRNA(mMet) derivatives containing the normal anticodon wobble base C. Base substitutions at this site decreased the Km for aminoacylation by the Phe461 mutant, while increasing the Km for the wild-type enzyme and for the Leu460 mutant to values greater than 100 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acyl-tRNA Synthetases↗
PubMed1979

Photocross-linking analysis of the contact surface of tRNA Met in complexes with Escherichia coli methionine:tRNA ligase.

Photoinduced covalent cross-linking has been used to identify a common surface of four methionine-accepting tRNAs which interact specifically with the Escherichia coli methionine:tRNA ligase (EC 6.1.1.10). tRNA--ligase mixtures were irradiated, and the covalently linked complexes were isolated and digested with T1 RNase (Schimmel & Budzik, 1977). The fragments lost from the elution profile of the T1 RNase digest were considered to have been cross-linked to the protein and therefore in intimate contact with the enzyme. Only specific cognate tRNA--ligase pairs produce covalently linked complexes. The four substrate tRNAs used in this study have substantially different sequences, but all showed a common cross-linking pattern, supporting the view that the sites cross-linked to the enzyme reflect the functionally common contact surface rather than particularly photoreactivity regions of tRNA. The cross-linked contact surface is comprised of three regions: (1) the narrow groove of the anticodon stem and its extension into the anticodon loop; (2) the 3' terminal residues; and (3) the 3' side of the "T arm". Unlike previous studies with other tRNAs, the D arm is not involved and significant radiation damage is suffered by the tRNA which must be taken into account in the analysis. The results are consistent with and complement chemical modification studies [Schulman, L. H., & Pelka, H. (1977) Biochemistry 16, 4256].

Amino Acyl-tRNA Synthetases↗
PubMed2003

Transiently misacylated tRNA is a primer for editing of misactivated adenylates by class I aminoacyl-tRNA synthetases.

The genetic code depends on amino acid fine structure discrimination by aminoacyl-tRNA synthetases. For isoleucyl- (IleRS) and valyl-tRNA synthetases (ValRS), reactions that hydrolyze misactivated noncognate amino acids help to achieve high accuracy in aminoacylation. Two editing pathways contribute to aminoacylation fidelity: pretransfer and post-transfer. In pretransfer editing, the misactivated amino acid is hydrolyzed as an aminoacyl adenylate, while in post-transfer editing a misacylated tRNA is deacylated. Both reactions are dependent on a tRNA cofactor and require translocation to a site located approximately 30 A from the site of amino acid activation. Using a series of 3'-end modified tRNAs that are deficient in either aminoacylation, deacylation, or both, total editing (the sum of pre- and post-transfer editing) was shown to require both aminoacylation and deacylation activities. These and additional results with IleRS are consistent with a post-transfer deacylation event initiating formation of an editing-active enzyme/tRNA complex. In this state, the primed complex processively edits misactivated valyl-adenylate via the pretransfer route. Thus, misacylated tRNA is an obligatory intermediate for editing by either pathway.

3' Flanking Region↗
PubMed1987

The isolation of a peptide from the catalytic domain of Bacillus stearothermophilus tryptophyl-tRNA synthetase. The interaction of Brown MX-5BR with tyrosyl-tRNA synthetase.

Tryptophyl-tRNA synthetase is irreversibly inactivated by Procion Brown MX-5BR with an apparent dissociation constant (KD) of 8.8 microM and maximum rate of inactivation k3 0.192 s-1. The specificity of the interaction is supported by two previously reported observations. Firstly, Brown MX-5BR inactivation of tryptophyl-tRNA synthetase is inhibited by substrates, and secondly, the animated derivative of Brown MX-5BR is a competitive inhibitor of tryptophyl-tRNA synthetase with a Ki of 2 X 10(-4) M with respect to both tryptophan and ATP. Tryptic digestion of the dye-affinity-labelled enzyme and subsequent resolution of the peptides by h.p.l.c. yielded one major dye-peptide peak. Amino acid sequence analysis resulted in the identification of the dye-binding domain centred on lysine-178. Tyrosyl-tRNA synthetase is also inactivated by Procion Brown MX-5BR, and this inactivation is prevented by ATP but not by tyrosine. The interaction of tyrosyl-tRNA synthetase with hydroxylated Brown MX-5BR exhibited non-competitive kinetics with respect to the amino acid-binding site and competitive kinetics against ATP with a Ki of 6 X 10(-6) M.

Amino Acid Sequence↗
PubMed2000

A domain in the N-terminal extension of class IIb eukaryotic aminoacyl-tRNA synthetases is important for tRNA binding.

Cytoplasmic aspartyl-tRNA synthetase (AspRS) from Saccharomyces cerevisiae is a homodimer of 64 kDa subunits. Previous studies have emphasized the high sensitivity of the N-terminal region to proteolytic cleavage, leading to truncated species that have lost the first 20-70 residues but that retain enzymatic activity and dimeric structure. In this work, we demonstrate that the N-terminal extension in yeast AspRS participates in tRNA binding and we generalize this finding to eukaryotic class IIb aminoacyl-tRNA synthetases. By gel retardation studies and footprinting experiments on yeast tRNA(Asp), we show that the extension, connected to the anticodon-binding module of the synthetase, contacts tRNA on the minor groove side of its anticodon stem. Sequence comparison of eukaryotic class IIb synthetases identifies a lysine-rich 11 residue sequence ((29)LSKKALKKLQK(39) in yeast AspRS with the consensus xSKxxLKKxxK in class IIb synthetases) that is important for this binding. Direct proof of the role of this sequence comes from a mutagenesis analysis and from binding studies using the isolated peptide.

Amino Acid Sequence↗