Dietary sources of free sugars in the diet of European children: the IDEFICS Study.

Objective: To report dietary free sugars consumption and their different types and food sources in European children.

Methods: The present study is based on the IDEFICS study, a European multicenter cohort study in children (2-9 years old) from eight countries, comprising 8308 children (51.4% males).

A marginal band of microtubules transports and organizes mitochondria in retinal bipolar synaptic terminals.

A set of bipolar cells in the retina of goldfish contains giant synaptic terminals that can be over 10 µm in diameter. Hundreds of thousands of synaptic vesicles fill these terminals and engage in continuous rounds of exocytosis. How the cytoskeleton and other organelles in these neurons are organized to control synaptic activity is unknown.

Mutations in residues involved in zinc binding in the catalytic site of Escherichia coli threonyl-tRNA synthetase confer a dominant lethal phenotype.

Escherichia coli threonyl-tRNA synthetase is a homodimeric protein that acts as both an enzyme and a regulator of gene expression: the protein aminoacylates tRNA(Thr) isoacceptors and binds to its own mRNA, inhibiting its translation. The enzyme contains a zinc atom in its active site, which is essential for the recognition of threonine. Mutations in any of the three amino acids forming the zinc-binding site inactivate the enzyme and have a dominant negative effect on growth if the corresponding genes are placed on a multicopy plasmid.

The N-terminal extension of Escherichia coli ribosomal protein L20 is important for ribosome assembly, but dispensable for translational feedback control.

The Escherichia coli autoregulatory ribosomal protein L20 consists of two structurally distinct domains. The C-terminal domain is globular and sits on the surface of the large ribosomal subunit whereas the N-terminal domain has an extended shape and penetrates deep into the RNA-rich core of the subunit. Many other ribosomal proteins have analogous internal or terminal extensions.

The modular structure of Escherichia coli threonyl-tRNA synthetase as both an enzyme and a regulator of gene expression.

In addition to its role in tRNA aminoacylation, Escherichia coli threonyl-tRNA synthetase is a regulatory protein which binds a site, called the operator, located in the leader of its own mRNA and inhibits translational initiation by competing with ribosome binding. This work shows that the two essential steps of regulation, operator recognition and inhibition of ribosome binding, are performed by different domains of the protein. The catalytic and the C-terminal domain of the protein are involved in binding the two anticodon arm-like structures in the operator whereas the N-terminal domain of the enzyme is responsible for the competition with the ribosome.

The relationship between translational control and mRNA degradation for the Escherichia coli threonyl-tRNA synthetase gene.

Expression of thrS, the gene encoding Escherichia coli threonyl-tRNA synthetase, is negatively autoregulated at the translational level. Regulation is due to the binding of threonyl-tRNA synthetase to its own mRNA at a site called the operator, located immediately upstream of the initiation codon. The present work investigates the relationship between regulation and mRNA degradation.

Discrimination by Escherichia coli initiation factor IF3 against initiation on non-canonical codons relies on complementarity rules.

Translation initiation factor IF3, one of three factors specifically required for translation initiation in Escherichia coli, inhibits initiation on any codon other than the three canonical initiation codons, AUG, GUG, or UUG. This discrimination against initiation on non-canonical codons could be due to either direct recognition of the two last bases of the codon and their cognate bases on the anticodon or to some ability to "feel" codon-anticodon complementarity. To investigate the importance of codon-anticodon complementarity in the discriminatory role of IF3, we constructed a derivative of tRNALeuthat has all the known characteristics of an initiator tRNA except the CAU anticodon.

Mutations that alter initiation codon discrimination by Escherichia coli initiation factor IF3.

This work describes the isolation of mutations in infC, the structural gene for IF3, using different genetic screens. Among 21 mutants characterised, seven were shown to produce stable variant IF3 proteins unable to fully complement a strain carrying a chromosomal deletion of the infC gene. The mutants were also shown to be unable to normally discriminate against several non-canonical initiation codons such as AUU and ACG.

The Escherichia coli threonyl-tRNA synthetase gene contains a split ribosomal binding site interrupted by a hairpin structure that is essential for autoregulation.

The expression of the gene encoding Escherichia coli threonyl-tRNA synthetase (ThrRS) is negatively autoregulated at the translational level. ThrRS binds to its own mRNA leader, which consists of four structural and functional domains: the Shine-Dalgarno (SD) sequence and the initiation codon region (domain 1); two upstream hairpins (domains 2 and 4) connected by a single-stranded region (domain 3). Using a combination of in vivo and in vitro approaches, we show here that the ribosome binds to thrS mRNA at two non-contiguous sites: region -12 to +16 comprising the SD sequence and the AUG codon and, unexpectedly, an upstream single-stranded sequence in domain 3.

The expression of E.coli threonyl-tRNA synthetase is regulated at the translational level by symmetrical operator-repressor interactions.

Threonyl-tRNA synthetase from Escherichia coli represses the translation of its own mRNA by binding to the operator region located upstream from the ribosome binding site. The operator contains two stemloop structures which interact specifically with the homodimeric enzyme. Here, we provide in vitro and in vivo evidence that these two stem-loop structures are recognized by the enzyme in an analogous way and mimic the anticodon arm of E.

Growth rate-dependent control, feedback regulation and steady-state mRNA levels of the threonyl-tRNA synthetase gene of Escherichia coli.

The expression of the gene thrS encoding threonyl-tRNA synthetase is under the control of two apparently different regulatory loops: translational feedback regulation and growth rate-dependent control. The translational feedback regulation is due to the binding of threonyl-tRNA synthetase to a site located in the leader RNA of thrS, upstream of the initiation codon, which mimics the anticodon stem and loop of tRNA(Thr). This binding competes with that of the ribosome and thus inhibits translation initiation.

The role of the AUU initiation codon in the negative feedback regulation of the gene for translation initiation factor IF3 in Escherichia coli.

The expression of the infC gene encoding translation initiation factor IF3 is negatively autoregulated at the level of translation, i.e. the expression of the gene is derepressed in a mutant infC background where the IF3 activity is lower than that of the wild type.

Physiological effects of translation initiation factor IF3 and ribosomal protein L20 limitation in Escherichia coli.

To investigate the physiological roles of translation initiation factor IF3 and ribosomal protein L20 in Escherichia coli, the infC, rpmI and rpIT genes encoding IF3, L35 and L20, respectively, were placed under the control of lac promotor/operator sequences. Thus, their expression is dependent upon the amount of inducer isopropyl thiogalactoside (IPTG) in the medium. Lysogenic strains were constructed with recombinant lambda phages that express either rpmI and rplT or infC and prmI in trans, thereby allowing depletion of only IF3 or L20 at low IPTG concentrations.

Stabilised secondary structure at a ribosomal binding site enhances translational repression in E. coli.

The expression of the gene encoding Escherichia coli threonyl-tRNA synthetase is negatively autoregulated at the translational level. The negative feedback is due to the binding of the synthetase to an operator site on its own mRNA located upstream of the initiation codon. The present work describes the characterisation of operator mutants that have the rare property of enhancing repression.

Messenger RNA secondary structure and translational coupling in the Escherichia coli operon encoding translation initiation factor IF3 and the ribosomal proteins, L35 and L20.

The Escherichia coli infC-rpmI-rplT operon encodes translation initiation factor IF3 and the ribosomal proteins, L35 and L20, respectively. The expression of the last cistron (rplT) has been shown to be negatively regulated at a post-transcriptional level by its own product, L20, which acts at an internal operator located within infC. The present work shows that L20 directly represses the expression of rpmI, and indirectly that of rplT, via translational coupling with rpmI.

Domains of the Escherichia coli threonyl-tRNA synthetase translational operator and their relation to threonine tRNA isoacceptors.

The expression of the gene for threonyl-tRNA synthetase (thrS) is negatively autoregulated at the translational level in Escherichia coli. The synthetase binds to a region of the thrS leader mRNA upstream from the ribosomal binding site inhibiting subsequent translation. The leader mRNA consists of four structural domains.

The specificity of translational control switched with transfer RNA identity rules.

The interaction of Escherichia coli threonyl-transfer RNA (tRNA) synthetase with the leader sequence of its own messenger RNA inhibits ribosome binding, resulting in negative translational feedback regulation. The leader sequence resembles the substrate (tRNA(Thr)) of the enzyme, and the nucleotides that mediate the correct recognition of the leader and the tRNA may be the same. A mutation suggested by tRNA identity rules that switches the resemblance of the leader sequence from tRNA(Thr) to tRNA(Met) causes the translation of the threonyl-tRNA synthetase messenger RNA to become regulated by methionyl-tRNA synthetase.

Translated translational operator in Escherichia coli. Auto-regulation in the infC-rpmI-rplT operon.

The genes coding for translation initiation factor IF3 (infC) and for the ribosomal proteins L35 (rpmI) and L20 (rplT) are transcribed in that order from a promoter in front of infC. The last two cistrons of the operon (rpmI and rplT) can be transcribed from a weak secondary promoter situated within the first cistron (infC). Previous experiments have shown that the expression of infC, the first cistron of the operon, is negatively autoregulated at the translational level and that the abnormal AUU initiation codon of infC is responsible for the control.

The relation between catalytic activity and gene regulation in the case of E coli threonyl-tRNA synthetase.

The expression of the gene for threonyl-tRNA synthetase (thrS) has previously been shown as being negatively autoregulated at the translational level. The region of the thrS leader mRNA responsible for that control is located immediately upstream of the ribosomal binding site, and was proposed to fold in a tRNA(Thr) anticodon arm-like structure. The present paper reviews experiments using enzymatic and chemical probes that prove the existence of a tRNA(Thr) anticodon-like structure in the thrS mRNA.

tRNA-like structures and gene regulation at the translational level: a case of molecular mimicry in Escherichia coli.

Escherichia coli threonyl-tRNA synthetase regulates the translation of its own mRNA by binding to it in a region, called the operator, located in front of the ribosomal binding site. The primary and secondary structures of the operator resemble those of the anticodon arm of several tRNA(Thr) isoacceptor species. We reasoned that if the interaction between the synthetase and its two partially analogous ligands, the tRNA and the mRNA, had some common features, single mutations in the enzyme should affect both interactions in a very similar way.

Translational control in E. coli: the case of threonyl-tRNA synthetase.

Genetic studies have shown that expression of the E. coli threonyl-tRNA synthetase (thrS) gene is negatively auto-regulated at the translational level. A region called the operator, located 110 nucleotides downstream of the 5' end of the mRNA and between 10 and 50 bp upstream of the translational initiation codon in the thrS gene, is directly involved in that control.

Open reading frames in the control regions of the phenylalanyl-tRNA synthetase operon of E. coli.

The pheST operon codes for the two subunits of phenylalanyl-tRNA synthetase and it expression is controlled by attenuation in a way similar to many amino acid biosynthetic operons. The nucleotide sequence of the control regions of the operon indicates the presence of several open reading frames besides that of the leader peptide. One of these open reading frames, called the alternative leader peptide, starts at about the same place as the leader peptide and ends after the terminator of the attenuator.

Escherichia coli protein synthesis initiation factor IF3 controls its own gene expression at the translational level in vivo.

Measurements of the relative synthesis rates of mRNAs transcribed from the gene (thrS) for threonyl-tRNA synthetase and the adjacent gene (infC) for initiation factor IF3 show four- to fivefold more infC mRNA than thrS mRNA in vivo, suggesting that infC expression can be controlled independently of thrS expression. S1 mapping experiments reveal the existence of two transcription initiation sites for infC mRNAs internal to the thrS structural gene. Both the mRNA measurements and the S1 mapping experiments indicate that the majority of infC transcription initiates at the infC proximal promoter.

Genetic definition of the translational operator of the threonine-tRNA ligase gene in Escherichia coli.

The Escherichia coli gene thrS that codes for threonine-tRNA ligase (tRNAThr ligase, formerly threonine-tRNA synthetase, EC 6.1.1.

Autogenous control of Escherichia coli threonyl-tRNA synthetase expression in vivo.

The regulation of the expression of thrS, the structural gene for threonyl-tRNA synthetase, was studied using several thrS-lac fusions cloned in lambda and integrated as single copies at att lambda. It is first shown that the level of beta-galactosidase synthesized from a thrS-lac protein fusion is increased when the chromosomal copy of thrS is mutated. It is also shown that the level of beta-galactosidase synthesized from the same protein fusion is decreased if wild-type threonyl-tRNA synthetase is overproduced from a thrS-carrying plasmid.