SEARCH · PubMed Health

Results for “Translational repression”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76Linked to original sources

PubMed1982

Regulation of adenylate cyclase synthesis in Escherichia coli: studies with cya-lac operon and protein fusion strains.

We have isolated cya-lac operon and protein fusions in Escherichia coli K-12, and we used these to study the regulation of cya, the structural gene for adenylate cyclase. Data obtained from these fusion strains suggest that neither cyclic AMP (cAMP) nor the cAMP receptor protein plays a major role in transcriptional or translational regulation of cya expression. Modulation of intracellular cAMP concentrations elicited only weak repression of cya-lac fusion activity under conditions of high intracellular cAMP, relative to fusion activity under conditions of low intracellular cAMP. The functional cAMP receptor protein was required for this effect. Incorporation of delta crp into cya-lac fusion strains did not affect fusion expression in glucose-grown cells as compared with similarly cultured isogenic crp+ strains. Furthermore, 20 independently obtained mutants derived from a cya-lacZ protein fusion strain exhibiting a weak Lac+ phenotype were isolated, and it was determined that the mutants had beta-galactosidase activities ranging from 2- to 77-fold greater than those of the parental strain. None of the mutations responsible for this increase in fusion activity map in the crp locus. We used these mutants to aid in the identification of a 160,000-dalton cya-lacZ hybrid protein. Finally, chromosome mobilization experiments, using cya-lac fusion strains, allowed us to infer a clockwise direction of transcription for the cya gene relative to the standard E. coli genetic map.

Adenylyl Cyclases↗

PubMed2006

Overexpression of tnaC of Escherichia coli inhibits growth by depleting tRNA2Pro availability.

Transcription of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. Induction results from ribosome stalling after translation of tnaC, the coding region for a 24-residue leader peptide. The last sense codon of tnaC, proline codon 24 (CCU), is translated by tRNA(2)(Pro). We analyzed the consequences of overexpression of tnaC from a multicopy plasmid and observed that under inducing conditions more than 60% of the tRNA(2)(Pro) in the cell was sequestered in ribosomes as TnaC-tRNA(2)(Pro). The half-life of this TnaC-tRNA(2)(Pro) was shown to be 10 to 15 min under these conditions. Plasmid-mediated overexpression of tnaC, under inducing conditions, reduced cell growth rate appreciably. Increasing the tRNA(2)(Pro) level relieved this growth inhibition, suggesting that depletion of this tRNA was primarily responsible for the growth rate reduction. Growth inhibition was not relieved by overexpression of tRNA(1)(Pro), a tRNA(Pro) that translates CCG, but not CCU. Replacing the Pro24CCU codon of tnaC by Pro24CCG, a Pro codon translated by tRNA(1)(Pro), also led to growth rate reduction, and this reduction was relieved by overexpression of tRNA(1)(Pro). These findings establish that the growth inhibition caused by tnaC overexpression during induction by tryptophan is primarily a consequence of tRNA(Pro) depletion, resulting from TnaC-tRNA(Pro) retention within stalled, translating ribosomes.

Escherichia coli↗

PubMed2005

RNA sequence and secondary structure participate in high-affinity CsrA-RNA interaction.

The global Csr regulatory system controls bacterial gene expression post-transcriptionally. CsrA of Escherichia coli is an RNA binding protein that plays a central role in repressing several stationary phase processes and activating certain exponential phase functions. CsrA regulates translation initiation of several genes by binding to the mRNA leaders and blocking ribosome binding. CsrB and CsrC are noncoding regulatory RNAs that are capable of sequestering CsrA and antagonizing its activity. Each of the known target transcripts contains multiple CsrA binding sites, although considerable sequence variation exists among these RNA targets, with GGA being the most highly conserved element. High-affinity RNA ligands containing single CsrA binding sites were identified from a combinatorial library using systematic evolution of ligands by exponential enrichment (SELEX). The SELEX-derived consensus was determined as RUACARGGAUGU, with the ACA and GGA motifs being 100% conserved and the GU sequence being present in all but one ligand. The majority (51/55) of the RNAs contained GGA in the loop of a hairpin within the most stable predicted structure, an arrangement similar to several natural CsrA binding sites. Strikingly, the identity of several nucleotides that were predicted to form base pairs in each stem were 100% conserved, suggesting that primary sequence information was embedded within the base-paired region. The affinity of CsrA for several selected ligands was measured using quantitative gel mobility shift assays. A mutational analysis of one selected ligand confirmed that the conserved ACA, GGA, and GU residues were critical for CsrA binding and that RNA secondary structure participates in CsrA-RNA recognition.

Bacterial Proteins↗

PubMed2005

Plant microRNAs and development.

MicroRNAs (miRNAs) act as negative regulators of gene expression in eukaryotes, a discovery that has opened an expanding field of biological research. Plant miRNAs are known to repress gene expression posttranscriptionally, mainly by guiding cleavage but also by attenuating the translation of target transcripts. In addition, it has been shown that plant miRNAs can also act at the transcriptional level by directing the methylation of target chromosomal loci. Genetic and biochemical approaches are quickly broadening our knowledge of the biogenesis and function of plant miRNAs. Computational approaches have uncovered an unexpectedly large number of miRNAs and their targets in plants. The targets of plant miRNAs often belong to families of transcription factors involved in the control of developmental processes. We review the status of research in this dynamic field, summarizing recent advances in our understanding of the biogenesis and mechanism of action of plant miRNAs, as well as in the developmental processes they regulate.

Base Sequence↗

PubMed1984

Structure and autoregulation of the metJ regulatory gene in Escherichia coli.

The nucleotide sequence of the Escherichia coli metJ regulatory gene (312 nucleotides) has been determined as well as that of two mutations located within the gene. Analysis of the sequence downstream from the metJ gene has revealed inverted repeats homologous to several intercistronic regions, also reported to occur between operons. A hybrid protein that contains the 55 first amino acid residues of the metJ protein substituting for the 8 amino acid residues at the NH2 terminus of beta-galactosidase was produced by gene fusion. The hybrid protein retaining beta-galactosidase activity was purified. Its amino-terminal sequence was determined and this allowed us to locate the translational start codon of the metJ gene. Evidence was provided for autoregulation by repression of the metJ gene. By sequencing upstream from metJ, the region situated between the metJ and metB genes was found to contain putative operator structures that we propose to call "Met boxes."

Alleles↗

PubMed1997

Multiple transcribed elements control expression of the Escherichia coli btuB gene.

Repression by vitamin B12 of the cobalamin transport protein BtuB in the outer membrane of Escherichia coli operates at both the transcriptional and translational levels and is controlled by transcribed sequences within the leader and proximal portion of the btuB coding sequence. The effects of deletions from either end of this region on repression and expression were determined with lac fusions. An element at the 5' end of the transcript and the putative attenuator within the coding sequence were required for transcriptional repression. The presence of either element caused a marked reduction in btuB-lacZ expression which was reversed by the presence of a conserved sequence element in the leader, suggesting the importance of long-range interactions in the btuB leader for expression and regulation.

Bacterial Outer Membrane Proteins↗

PubMed1985

Mitochondrial transcription and processing of transcripts during release from glucose repression in 'resting cells' of Saccharomyces cerevisiae.

Mitochondrial transcription and processing of transcripts have been investigated at different stages of release from glucose repression in resting cells of Saccharomyces cerevisiae. Transcripts were identified by hybridization with nick-translated or terminally labelled gene-specific probes. This allowed the determination of the steady-state levels of individual transcripts in the mitochondrial RNA population. Results showed different gene-specific patterns of response to respiratory induction: no increase in the level of transcripts (oxi2); a rapid increase in the steady-state levels of all transcripts (cob); a very strong increase in the processing of the high-molecular-mass precursors (oxi3 and oli2); an increase in the level of stable circular transcripts (oxi3). As a whole the results indicate specific and differentiated effects of release from glucose repression on the expression of the different mitochondrial genes and demonstrate the importance of processing events in mitochondrial regulation.

Autoradiography↗

PubMed1997

H1-mediated repression of transcription factor binding to a stably positioned nucleosome.

Previously, we reported that histone H1 binding to nucleosome cores results in the repression of binding of the basic helix-loop-helix upstream stimulatory factor (USF) (Juan, L.-J., Utley, R. T., Adams, C. C., Vettese-Dadey, M., and Workman, J. L. (1994) EMBO J. 13, 6031-6040). We have tested whether this inhibition resulted from H1-mediated changes in nucleosome positioning (Ura, K., Hayes, J. J., and Wolffe, A. P. (1995) EMBO J. 14, 3752-3765) forcing the USF recognition sequence into less accessible locations within the nucleosome. Nucleosome boundaries were determined by assays combining micrococcal nuclease and restriction endonuclease digestion. A unique pair of boundaries were observed, indicating a single nucleosome translational position. This nucleosome position did not change on H1 or USF binding. Thus, H1 repression of USF binding was independent of nucleosome mobility, indicating an alternative mechanism of H1 repression. H1 repressed USF binding at a site 35 base pairs into the nucleosome core more effectively than at a site near the "linker" DNA, suggesting that inhibition by H1 was not simply due to steric occlusion. Instead, these data are consistent with a model by which H1 binding reduces transient dynamic exposure of the DNA from the histone octamer surface (Polach, K. L., and Widom, J. (1995) J. Mol. Biol. 254, 130-149).

Binding Sites↗

PubMed1976

Suppression of temperature-sensitive aminoacyl-tRNA synthetase mutations by ribosomal mutations: a possible mechanism.

The biochemical basis of suppression of a temperature-sensitive alanyl-tRNA synthetase (alaS) mutation by mutational alterations of the ribosome has been investigated. Measurement of the polyU-dependent polyphenylalanine synthesis showed that ribosomes from the suppressor strains are less active than ribosomes from the unsuppressed aminoacyl-tRNA synthetase mutant. In this system no increased translational ambiguity could be detected for the suppressor ribosomes. This fact and also the findings that the ram-1 mutation is not able to suppress the aminoacyl-tRNA synthetase mutation and that presence of the suppressor allele is not accompanied by a measureably improved alanyl-tRNA synthetase activity argue against the possibility that suppression might be due to increased translational misreading rates of the alanyl-tRNA synthetase mRNA. It has been further found that partial suppression of temperature sensitive growth of the alaS mutation can be achieved by independent ribosomal mutations leading to reduced growth rates because of a mutation to antibiotic resistance. Addition of low concentrations of a variety of antibiotics acting at the ribosomal level can also partially revert the temperature-sensitive phenotype of the alaS mutant. Although the possibility cannot be excluded that suppression is due to the stabilisation or activation of the mutant enzyme by some indirect effect of the suppressor ribosomal mutations, the following working hypothesis is favoured at the moment: It is assumed that limitation of the aminoacyl-tRNA synthetase activity in a certain range of the restrictive temperature causes growth inhibition by the premature termination of polypeptide synthesis at the ribosome or by the unbalanced synthesis of the individual cellular proteins under this condition. The mechanism of suppression by ribosomal mutations is proposed to consist of the release of this growth inhibition by the reduction of the rate of polypeptide synthesis, which would keep amino acid incorporation from exceeding the slow charging of tRNA and thus exhausting the pool of charged tRNA. In the suppressor strains, therefore, growth at the semi-restrictive temperature is no longer limited by the aminoacylation of tRNA but by the translational process at the mutated ribosome. This influence of the ribosomal mutation on the speed of translation could be directly or indirectly coupled with an effect on translational fidelity resulting in the prevention of the binding of uncharged or non-cognate charged tRNA or in the tighter binding of peptidyl-tRNA when cognate aminoacyl-tRNA is limiting.

Alanine-tRNA Ligase↗

PubMed1981

Control of expression of the vaccinia virus thymidine kinase gene.

mRNA extracted from vaccinia virus-infected cells early after infection directs cell-free synthesis of enzymatically active viral thymidine kinase (Hruby and Ball, Virology, in press). We used this assay for a specific vaccinia virus mRNA to study the induction and repression of the viral thymidine kinase gene during infection of thymidine kinase-deficient L-cells. As observed previously by other workers, the synthesis of thymidine kinase occurred immediately after infection but was switched off after 4 h later. We observed similar kinetics of accumulation and shutoff under conditions where viral DNA synthesis and late gene expression were inhibited. Cell-free translation of mRNA from infected cells showed that the concentration of functional message for viral thymidine kinase reached a peak 3 to 4 h after infection and then decreased with a half-life of about 1 h. These kinetics indicated that significant levels of thymidine kinase mRNA persisted in cells which had stopped synthesizing the enzyme. Under conditions where late gene expression was inhibited, high concentrations of functional mRNA could be isolated from cells at late times after infection. On the basis of these results, we conclude that the repression of thymidine kinase expression is mediated at the translational level by one or more early or delayed early viral genes. Repression is accompanied by, but does not depend on, the inactivation or degradation of thymidine kinase mRNA, which is a late gene function.

Animals↗

PubMed2004

eEF1A binding to aminoacylated viral RNA represses minus strand synthesis by TYMV RNA-dependent RNA polymerase.

The genomic RNA of Turnip yellow mosaic virus (TYMV) has an 82-nucleotide-long tRNA-like structure at its 3'-end that can be valylated and then form a stable complex with translation elongation factor eEF1A.GTP. Transcription of this RNA by TYMV RNA-dependent RNA polymerase (RdRp) to yield minus strands has previously been shown to initiate within the 3'-CCA sequence. We have now demonstrated that minus strand synthesis is strongly repressed upon the binding of eEF1A.GTP to the valylated viral RNA. eEF1A.GTP had no effect on RNA synthesis templated by non-aminoacylated RNA. Higher eEF1A.GTP levels were needed to repress minus strand synthesis templated by valyl-EMV TLS RNA, which binds eEF1A.GTP with lower affinity than does valyl-TYMV RNA. Repression by eEF1A.GTP was also observed with a methionylated variant of TYMV RNA and with aminoacylated tRNAHis, tRNAAla, and tRNAPhe transcripts. It is proposed that minus strand repression by eEF1A.GTP binding occurs early during infection to help coordinate the competing translation and replication functions of the genomic RNA.

Acylation↗

PubMed1988

Rapid turnover of adenovirus E1A is determined through a co-translational mechanism that requires an aminoterminal domain.

The product of the adenovirus E1A 13S mRNA can both stimulate and repress the expression of certain viral and cellular genes. As with several other regulatory proteins, E1A has a short half-life, approximately 40 min. Although this short half-life is observed in cells expressing the E1A gene, it is not the case with cells injected with E1A protein, where its half-life is very long, generally greater than 15 h. We have sought to reconcile these apparent differences in E1A stability. Using Xenopus oocytes, we find that E1A exhibits its characteristic short half-life when it is synthesized from injected mRNA while it has a very long half-life when it is injected as a protein synthesized originally in Escherichia coli or reticulocyte lysates. In order to delineate the amino acids responsible for rapid E1A turnover, several deletion mRNAs were constructed, injected into oocytes, and E1A half-life determined. Carboxyl-terminal deletions and an internal deletion of residues 38-86 failed to increase the half-life of E1A. In contrast, amino-terminal deletions of 70 and 14 residues resulted in very stable E1A proteins (t1/2 greater than 20 h). Furthermore, deletion of the second amino acid, an arginine, resulted in a stable E1A protein. The amino-terminal region of E1A was able to induce the rapid turnover of a normally stable protein, beta-globin, in oocytes injected with an E1A-globin chimeric mRNA. This E1A-induced instability of globin was abolished, however, when the protein was first synthesized in reticulocyte lysates and then injected into oocytes. The amino-terminal region of E1A is also important in governing halflife in adenovirus-infected HeLa cells. These results demonstrate that the half-life of E1A is established cotranslationally through a mechanism involving sequences within the amino-terminal 37 residues.

Adenovirus Early Proteins↗

PubMed1999

Translation of maternal TATA-binding protein mRNA potentiates basal but not activated transcription in Xenopus embryos at the midblastula transition.

Early embryonic development in Xenopus laevis is characterized by transcriptional repression which is relieved at the midblastula stage (MBT). Here we show that the relative abundance of TATA-binding protein (TBP) increases robustly at the MBT and that the mechanism underlying this increase is translation of maternally stored TBP RNA. We show that TBP is rate-limiting in egg extract under conditions that titrate nucleosome assembly. Precocious translation of TBP mRNA in Xenopus embryos facilitates transcription before the MBT, without requiring TBP to be prebound to the promoter before injection. This effect is transient in the absence of chromatin titration and is sustained when chromatin is titrated. These data show that translational regulation of TBP RNA contributes to limitations on the transcriptional capacity before the MBT. Second, we examined the ability of trans-acting factors to contribute to promoter activity before the MBT. Deletion of cis-acting elements does not affect histone H2B transcription in egg extract, a finding indicative of limited trans-activation. Moreover, in the context of the intact promoter, neither the transcriptional activator Oct-1, nor TBP, nor TFIID enable transcriptional activation in vitro. HeLa cell extract, however, reconstitutes activated transcription in mixed extracts. These data suggest a deficiency in egg extract cofactors required for activated transcription. We show that the capacity for activated H2B transcription is gradually acquired at the early gastrula transition. This transition occurs well after the blastula stage when the basal transcription machinery can first be complemented with TBP.

Animals↗

PubMed1996

Translational initiation competence, 'leaky scanning' and translational reinitiation in areA mRNA of Aspergillus nidulans.

(1) AUG codons that either permit or prevent 'leaky scanning' of mRNA encoding AREA, the transcriptional activator mediating nitrogen metabolite repression in Aspergillus nidulans, have been identified. The consensus context for a strong initiation codon (i.e. one preventing 'leaky scanning') derived from this work is GXX AUG C/UCX. However, AUG codons which do not conform to this consensus are nevertheless able to initiate translation. (2) Translational reinitiation can occur within areA mRNA, although there is a limitation determined by the distance between the chain termination and reinitiation codons and/or the strength of the reinitiation codon. (3) The minimum size of the region of areA mRNA that is competent for initiation of translation has been determined to be 329 nucleotides (nt), and might be at least 975 nt if a 709 bp deletion does not alter it.

Amino Acid Sequence↗

PubMed2000

The last RNA-binding repeat of the Escherichia coli ribosomal protein S1 is specifically involved in autogenous control.

The ssyF29 mutation, originally selected as an extragenic suppressor of a protein export defect, has been mapped within the rpsA gene encoding ribosomal protein S1. Here, we examine the nature of this mutation and its effect on translation. Sequencing of the rpsA gene from the ssyF mutant has revealed that, due to an IS10R insertion, its product lacks the last 92 residues of the wild-type S1 protein corresponding to one of the four homologous repeats of the RNA-binding domain. To investigate how this truncation affects translation, we have created two series of Escherichia coli strains (rpsA(+) and ssyF) bearing various translation initiation regions (TIRs) fused to the chromosomal lacZ gene. Using a beta-galactosidase assay, we show that none of these TIRs differ in activity between ssyF and rpsA(+) cells, except for the rpsA TIR: the latter is stimulated threefold in ssyF cells, provided it retains at least ca. 90 nucleotides upstream of the start codon. Similarly, the activity of this TIR can be severely repressed in trans by excess S1, again provided it retains the same minimal upstream sequence. Thus, the ssyF stimulation requires the presence of the rpsA translational autogenous operator. As an interpretation, we propose that the ssyF mutation relieves the residual repression caused by normal supply of S1 (i.e., that it impairs autogenous control). Thus, the C-terminal repeat of the S1 RNA-binding domain appears to be required for autoregulation, but not for overall mRNA recognition.

Amino Acid Sequence↗

PubMed2002

Coupling of the dolichol-P-P-oligosaccharide pathway to translation by perturbation-sensitive regulation of the initiating enzyme, GlcNAc-1-P transferase.

In mammalian cells, inhibition of translation interferes with synthesis of the lipid-linked oligosaccharide (LLO) Glc3Man9GlcNAc2-P-P-dolichol as measured with radioactive sugar precursors. Conflicting hypotheses have been proposed, and the fundamental basis for this regulation has remained elusive. Here, fluorophore-assisted carbohydrate electrophoresis (FACE) was used to measure LLO concentrations directly in cells treated with translation blockers. Further, LLO biosynthetic enzymes were assayed in vitro with endogenous acceptor substrates using either cells gently permeabilized with streptolysin-O (SLO) or microsomes from homogenized cells. In Chinese hamster ovary (CHO)-K1 cells treated with translation blockers, FACE did not detect changes in concentrations of Glc3Man9GlcNAc2-P-P-dolichol or early LLO intermediates. These results do not support earlier proposals for feedback repression of LLO initiation by accumulated Glc3Man9GlcNAc2-P-P-dolichol, or inhibition of a GDP-mannose dependent transferase. With microsomes from cells treated with translation blockers, there was no interference with LLO initiation by GlcNAc-1-P transferase (GPT), mannose-P-dolichol synthase, glucose-P-dolichol synthase, or LLO synthesis in vitro, as reported previously. Surprisingly, inhibition of all of these was detected with the SLO in vitro system. Additional experiments with the SLO system showed that the three transferases shared a limited pool of dolichol-P that was trapped as Glc3Man9GlcNAc2-P-P-dolichol by translation arrest. Overexpression of GPT was unable to reverse the effects of translation arrest on LLO initiation, and experiments with FACE and the SLO system showed that overexpressed GPT was not functional in vivo, although it was highly active in microsomal assays. Thus, the combined use of the SLO in vitro system and FACE showed that LLO biosynthesis depends upon a limited primary pool of dolichol-P. Physical perturbation associated with microsome preparation appears to make available a secondary pool of dolichol-P, masking inhibition by translation arrest, as well as activating a nonfunctional fraction of GPT. The implications of these results for the organization of the LLO pathway are discussed.

Animals↗

PubMed2001

A novel role for the Bcl-2 protein family: specific suppression of the RAD51 recombination pathway.

The oncogenic role of Bcl-2 is generally attributed to its protective effect against apoptosis. Here, we show a novel role for Bcl-2: the specific inhibition of the conservative RAD51 recombination pathway. Bcl-2 or Bcl-X(L) overexpression inhibits UV-C-, gamma-ray- or mutant p53-induced homologous recombination (HR). Moreover, Bcl-2 recombination inhibition is independent of the role of p53 in G1 arrest. At an acute double-strand break in the recombination substrate, Bcl-2 specifically inhibits RAD51-dependent gene conversion without affecting non-conservative recombination. Bcl-2 consistently thwarts recombination stimulated by RAD51 overexpression and alters Rad51 protein by post-translation modification. Moreover, a mutant (G145A)Bcl-2, which is defective in Bax interaction and in apoptosis repression, also inhibits recombination, showing that the death and recombination repression functions of Bcl-2 are separable. Inhibition of error-free repair pathways by Bcl-2 results in elevated frequencies of mutagenesis. The Bcl-2 gene therefore combines two separable cancer-prone phenotypes: apoptosis repression and a genetic instability/mutator phenotype. This dual phenotype could represent a mammalian version of the bacterial SOS repair system.

Animals↗

PubMed2025

High temperature-responsive DEAR4 condensation confers thermotolerance through recruiting TOPLESS in Arabidopsis nucleus.

Global warming is harmful to plants and threatens crop yields in the world. In contrast to other abiotic stresses, the molecular mechanisms for plant high temperature perception and signaling are still not fully understood. Here, we report that transcription factor DREB AND EAR MOTIF PROTEIN 4 (DEAR4) positively regulates heat tolerance in Arabidopsis thaliana. We further reveal that DEAR4 proteins undergo liquid-liquid phase separation (LLPS) and high temperature could induce DEAR4 condensate formation in the nucleus. Moreover, DEAR4 recruits the transcriptional co-repressor TOPLESS (TPL) into the nuclear speckles under high temperature. The high temperature triggered DEAR4-TPL co-condensates enhance their transcriptional repression activity through modulating histone deacetylation levels of GASA5, which is a reported negative regulator of HEAT SHOCK PROTEINs (HSPs). A genome-wide transcriptional landscape study confirms that DEAR4 induces the expression of multiple HSPs. Taken together, we illustrate a transcriptional repression mechanism mediated by DEAR4 through LLPS to confer plants thermotolerance and open a new avenue for translating this knowledge into crops for improving their heat resistance.

Arabidopsis↗