1
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Warner BR, Fredrick K. Contribution of an alternative 16S rRNA helix to biogenesis of the 30S subunit of the ribosome. RNA (NEW YORK, N.Y.) 2024; 30:770-778. [PMID: 38570183 PMCID: PMC11182017 DOI: 10.1261/rna.079960.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 03/23/2024] [Indexed: 04/05/2024]
Abstract
30S subunits become inactive upon exposure to low Mg2+ concentration, because of a reversible conformational change that entails nucleotides (nt) in the neck helix (h28) and 3' tail of 16S rRNA. This active-to-inactive transition involves partial unwinding of h28 and repairing of nt 921-923 with nt 1532-1534, which requires flipping of the 3' tail by ∼180°. Growing evidence suggests that immature 30S particles adopt the inactive conformation in the cell, and transition to the active state occurs at a late stage of maturation. Here, we target nucleotides that form the alternative helix (hALT) of the inactive state. Using an orthogonal ribosome system, we find that disruption of hALT decreases translation activity in the cell modestly, by approximately twofold, without compromising ribosome fidelity. Ribosomes carrying substitutions at positions 1532-1533 support the growth of Escherichia coli strain Δ7 prrn (which carries a single rRNA operon), albeit at rates 10%-20% slower than wild-type ribosomes. These mutant Δ7 prrn strains accumulate free 30S particles and precursor 17S rRNA, indicative of biogenesis defects. Analysis of purified control and mutant subunits suggests that hALT stabilizes the inactive state by 1.2 kcal/mol with little-to-no impact on the active state or the transition state of conversion.
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Affiliation(s)
- Benjamin R Warner
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
| | - Kurt Fredrick
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
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2
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Chadani Y, Kanamori T, Niwa T, Ichihara K, Nakayama KI, Matsumoto A, Taguchi H. Mechanistic dissection of premature translation termination induced by acidic residues-enriched nascent peptide. Cell Rep 2023; 42:113569. [PMID: 38071619 DOI: 10.1016/j.celrep.2023.113569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 10/18/2023] [Accepted: 11/24/2023] [Indexed: 12/30/2023] Open
Abstract
Ribosomes polymerize nascent peptides through repeated inter-subunit rearrangements between the classic and hybrid states. The peptidyl-tRNA, the intermediate species during translation elongation, stabilizes the translating ribosome to ensure robust continuity of elongation. However, the translation of acidic residue-rich sequences destabilizes the ribosome, leading to a stochastic premature translation cessation termed intrinsic ribosome destabilization (IRD), which is still ill-defined. Here, we dissect the molecular mechanisms underlying IRD in Escherichia coli. Reconstitution of the IRD event reveals that (1) the prolonged ribosome stalling enhances IRD-mediated translation discontinuation, (2) IRD depends on temperature, (3) the destabilized 70S ribosome complex is not necessarily split, and (4) the destabilized ribosome is subjected to peptidyl-tRNA hydrolase-mediated hydrolysis of the peptidyl-tRNA without subunit splitting or recycling factors-mediated subunit splitting. Collectively, our data indicate that the translation of acidic-rich sequences alters the conformation of the 70S ribosome to an aberrant state that allows the noncanonical premature termination.
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Affiliation(s)
- Yuhei Chadani
- Faculty of Environmental, Life, Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
| | | | - Tatsuya Niwa
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; School of Life Science and Technology, Tokyo Institute of Technology, Yokohama 226-8503, Japan
| | - Kazuya Ichihara
- Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
| | - Keiichi I Nakayama
- Anticancer Strategies Laboratory, TMDU Advanced Research Institute, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8510, Japan; Division of Cell Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan
| | - Akinobu Matsumoto
- Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
| | - Hideki Taguchi
- Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan; School of Life Science and Technology, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
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3
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Nguyen H, Hoffer E, Fagan C, Maehigashi T, Dunham C. Structural basis for reduced ribosomal A-site fidelity in response to P-site codon-anticodon mismatches. J Biol Chem 2023; 299:104608. [PMID: 36924943 PMCID: PMC10140155 DOI: 10.1016/j.jbc.2023.104608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 03/10/2023] [Accepted: 03/11/2023] [Indexed: 03/16/2023] Open
Abstract
Rapid and accurate translation is essential in all organisms to produce properly folded and functional proteins. mRNA codons that define the protein coding sequences are decoded by tRNAs on the ribosome in the aminoacyl (A) binding site. The mRNA codon and the tRNA anticodon interaction is extensively monitored by the ribosome to ensure accuracy in tRNA selection. While other polymerases that synthesize DNA and RNA can correct for misincorporations, the ribosome is unable to correct mistakes. Instead, when a misincorporation occurs, the mismatched tRNA-mRNA pair moves to the peptidyl (P) site and from this location, causes a reduction in the fidelity at the A site, triggering post-peptidyl transfer quality control. This reduced fidelity allows for additional incorrect tRNAs to be accepted and for release factor 2 (RF2) to recognize sense codons, leading to hydrolysis of the aberrant peptide. Here, we present crystal structures of the ribosome containing a tRNALys in the P site with a U•U mismatch with the mRNA codon. We find that when the mismatch occurs in the second position of the P-site codon-anticodon interaction, the first nucleotide of the A-site codon flips from the mRNA path to engage highly conserved 16S rRNA nucleotide A1493 in the decoding center. We propose that this mRNA nucleotide mispositioning leads to reduced fidelity at the A site. Further, this state may provide an opportunity for RF2 to initiate premature termination before erroneous nascent chains disrupt the cellular proteome.
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Affiliation(s)
- HaAn Nguyen
- Department of Chemistry, Emory University, Atlanta, GA USA; Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
| | - EricD Hoffer
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA; Biochemistry, Cell and Developmental Biology Graduate Program, Emory University, Atlanta, GA USA
| | - CrystalE Fagan
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA; Biochemistry, Cell and Developmental Biology Graduate Program, Emory University, Atlanta, GA USA
| | - Tatsuya Maehigashi
- Department of Chemistry, Emory University, Atlanta, GA USA; Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
| | - ChristineM Dunham
- Department of Chemistry, Emory University, Atlanta, GA USA; Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA.
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4
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Nguyen HA, Hoffer ED, Fagan CE, Maehigashi T, Dunham CM. Structural basis for reduced ribosomal A-site fidelity in response to P-site codon-anticodon mismatches. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.28.526049. [PMID: 36747737 PMCID: PMC9900946 DOI: 10.1101/2023.01.28.526049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Rapid and accurate translation is essential in all organisms to produce properly folded and functional proteins. mRNA codons that define the protein coding sequences are decoded by tRNAs on the ribosome in the aminoacyl (A) binding site. The mRNA codon and the tRNA anticodon interaction is extensively monitored by the ribosome to ensure accuracy in tRNA selection. While other polymerases that synthesize DNA and RNA can correct for misincorporations, the ribosome is unable to correct mistakes. Instead, when a misincorporation occurs, the mismatched tRNA-mRNA pair moves to the peptidyl (P) site and from this location, causes a reduction in the fidelity at the A site, triggering post-peptidyl transfer quality control. This reduced fidelity allows for additional incorrect tRNAs to be accepted and for release factor 2 (RF2) to recognize sense codons, leading to hydrolysis of the aberrant peptide. Here, we present crystal structures of the ribosome containing a tRNA Lys in the P site with a U•U mismatch with the mRNA codon. We find that when the mismatch occurs in the second position of the P-site codon-anticodon interaction, the first nucleotide of the A-site codon flips from the mRNA path to engage highly conserved 16S rRNA nucleotide A1493 in the decoding center. We propose that this mRNA nucleotide mispositioning leads to reduced fidelity at the A site. Further, this state may provide an opportunity for RF2 to initiate premature termination before erroneous nascent chains disrupt the cellular proteome.
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Affiliation(s)
- Ha An Nguyen
- Department of Chemistry, Emory University, Atlanta, GA USA
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
| | - Eric D. Hoffer
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
- Biochemistry, Cell and Developmental Biology Graduate Program, Emory University, Atlanta, GA USA
| | - Crystal E. Fagan
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
- Biochemistry, Cell and Developmental Biology Graduate Program, Emory University, Atlanta, GA USA
| | - Tatsuya Maehigashi
- Department of Chemistry, Emory University, Atlanta, GA USA
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
| | - Christine M. Dunham
- Department of Chemistry, Emory University, Atlanta, GA USA
- Emory Antibiotic Resistance Center (ARC), Emory University, Atlanta, GA USA
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5
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Wakabayashi H, Warnasooriya C, Ermolenko DN. Extending the Spacing between the Shine-Dalgarno Sequence and P-Site Codon Reduces the Rate of mRNA Translocation. J Mol Biol 2020; 432:4612-4622. [PMID: 32544497 DOI: 10.1016/j.jmb.2020.06.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 06/08/2020] [Accepted: 06/09/2020] [Indexed: 12/24/2022]
Abstract
By forming base-pairing interactions with the 3' end of 16S rRNA, mRNA Shine-Dalgarno (SD) sequences positioned upstream of open reading frames facilitate translation initiation. During the elongation phase of protein synthesis, intragenic SD-like sequences stimulate ribosome frameshifting and may also slow down ribosome movement along mRNA. Here, we show that the length of the spacer between the SD sequence and P-site codon strongly affects the rate of ribosome translocation. Increasing the spacer length beyond 6 nt destabilizes mRNA-tRNA-ribosome interactions and results in a 5- to 10-fold reduction of the translocation rate. These observations suggest that during translation, the spacer between the SD sequence and P-site codon undergoes structural rearrangements, which slow down mRNA translocation and promote mRNA frameshifting.
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Affiliation(s)
- Hironao Wakabayashi
- Department of Biochemistry & Biophysics at School of Medicine and Dentistry and Center for RNA Biology, University of Rochester, Rochester, NY 14642, USA
| | - Chandani Warnasooriya
- Department of Biochemistry & Biophysics at School of Medicine and Dentistry and Center for RNA Biology, University of Rochester, Rochester, NY 14642, USA
| | - Dmitri N Ermolenko
- Department of Biochemistry & Biophysics at School of Medicine and Dentistry and Center for RNA Biology, University of Rochester, Rochester, NY 14642, USA.
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6
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Ying L, Zhu H, Shoji S, Fredrick K. Roles of specific aminoglycoside-ribosome interactions in the inhibition of translation. RNA (NEW YORK, N.Y.) 2019; 25:247-254. [PMID: 30413565 PMCID: PMC6348987 DOI: 10.1261/rna.068460.118] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 11/06/2018] [Indexed: 05/18/2023]
Abstract
Aminoglycosides containing a 2-deoxystreptamine core (AGs) represent a large family of antibiotics that target the ribosome. These compounds promote miscoding, inhibit translocation, and inhibit ribosome recycling. AG binding to helix h44 of the small subunit induces rearrangement of A-site nucleotides A1492 and A1493, which promotes a key open-to-closed conformational change of the subunit and thereby increases miscoding. Mechanisms by which AGs inhibit translocation and recycling remain less clear. Structural studies have revealed a secondary AG binding site in H69 of the large subunit, and it has been proposed that interaction at this site is crucial for inhibition of translocation and recycling. Here, we analyze ribosomes with mutations targeting either or both AG binding sites. Assaying translocation, we find that ablation of the h44 site increases the IC50 values for AGs dramatically, while removal of the H69 site increases these values modestly. This suggests that the AG-h44 interaction is primarily responsible for inhibition, with H69 playing a minor role. Assaying recycling, we find that mutation of h44 has no effect on AG inhibition, consistent with a primary role for AG-H69 interaction. Collectively, these findings help clarify the roles of the two AG binding sites in mechanisms of inhibition by these compounds.
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Affiliation(s)
- Lanqing Ying
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
| | - Hongkun Zhu
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
| | - Shinichiro Shoji
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
| | - Kurt Fredrick
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
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7
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Roy B, Liu Q, Shoji S, Fredrick K. IF2 and unique features of initiator tRNA fMet help establish the translational reading frame. RNA Biol 2017; 15:604-613. [PMID: 28914580 DOI: 10.1080/15476286.2017.1379636] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Translation begins at AUG, GUG, or UUG codons in bacteria. Start codon recognition occurs in the P site, which may help explain this first-position degeneracy. However, the molecular basis of start codon specificity remains unclear. In this study, we measured the codon dependence of 30S•mRNA•tRNAfMet and 30S•mRNA•tRNAMet complex formation. We found that complex stability varies over a large range with initiator tRNAfMet, following the same trend as reported previously for initiation rate in vivo (AUG > GUG, UUG > CUG, AUC, AUA > ACG). With elongator tRNAMet, the codon dependence of binding differs qualitatively, with virtually no discrimination between GUG and CUG. A unique feature of initiator tRNAfMet is a series of three G-C basepairs in the anticodon stem, which are known to be important for efficient initiation in vivo. A mutation targeting the central of these G-C basepairs causes the mRNA binding specificity pattern to change in a way reminiscent of elongator tRNAMet. Unexpectedly, for certain complexes containing fMet-tRNAfMet, we observed mispositioning of mRNA, such that codon 2 is no longer programmed in the A site. This mRNA mispositioning is exacerbated by the anticodon stem mutation and suppressed by IF2. These findings suggest that both IF2 and the unique anticodon stem of fMet-tRNAfMet help constrain mRNA positioning to set the correct reading frame during initiation.
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Affiliation(s)
- Bappaditya Roy
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Qi Liu
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Shinichiro Shoji
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
| | - Kurt Fredrick
- a Department of Microbiology and Center for RNA Biology , Ohio State University , Columbus , Ohio , USA
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8
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Zinoviev A, Hellen CUT, Pestova TV. Multiple mechanisms of reinitiation on bicistronic calicivirus mRNAs. Mol Cell 2016; 57:1059-1073. [PMID: 25794616 DOI: 10.1016/j.molcel.2015.01.039] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 12/31/2014] [Accepted: 01/26/2015] [Indexed: 02/05/2023]
Abstract
Reinitiation is a strategy used by viruses to express several cistrons from one mRNA. Although extremely weak after translation of long open reading frames (ORFs) on cellular mRNAs, reinitiation occurs efficiently on subgenomic bicistronic calicivirus mRNAs, enabling synthesis of minor capsid proteins. The process is governed by a short element upstream of the restart AUG, designated "termination upstream ribosomal binding site" (TURBS). It contains the conserved Motif 1 complementary to h26 of 18S rRNA, displayed in the loop of a hairpin formed by species-specific Motifs 2/2(∗). To determine the advantages conferred on reinitiation by TURBS, we reconstituted this process in vitro on two model bicistronic calicivirus mRNAs. We found that post-termination ribosomal tethering of mRNA by TURBS allows reinitiation by post-termination 80S ribosomes and diminishes dependence on eukaryotic initiation factor 3 (eIF3) of reinitiation by recycled 40S subunits, which can be mediated either by eIFs 2/1/1A or by Ligatin following ABCE1-dependent or -independent splitting of post-termination complexes.
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Affiliation(s)
- Alexandra Zinoviev
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
| | - Christopher U T Hellen
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
| | - Tatyana V Pestova
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
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9
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Ying L, Fredrick K. Epistasis analysis of 16S rRNA ram mutations helps define the conformational dynamics of the ribosome that influence decoding. RNA (NEW YORK, N.Y.) 2016; 22:499-505. [PMID: 26873598 PMCID: PMC4793206 DOI: 10.1261/rna.054486.115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 01/14/2016] [Indexed: 06/05/2023]
Abstract
The ribosome actively participates in decoding, with a tRNA-dependent rearrangement of the 30S A site playing a key role. Ribosomal ambiguity (ram) mutations have mapped not only to the A site but also to the h12/S4/S5 region and intersubunit bridge B8, implicating other conformational changes such as 30S shoulder rotation and B8 disruption in the mechanism of decoding. Recent crystallographic data have revealed that mutation G299A in helix h12 allosterically promotes B8 disruption, raising the question of whether G299A and/or other ram mutations act mainly via B8. Here, we compared the effects of each of several ram mutations in the absence and presence of mutation h8Δ2, which effectively takes out bridge B8. The data obtained suggest that a subset of mutations including G299A act in part via B8 but predominantly through another mechanism. We also found that G299A in h12 and G347U in h14 each stabilize tRNA in the A site. Collectively, these data support a model in which rearrangement of the 30S A site, inward shoulder rotation, and bridge B8 disruption are loosely coupled events, all of which promote progression along the productive pathway toward peptide bond formation.
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Affiliation(s)
- Lanqing Ying
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
| | - Kurt Fredrick
- Department of Microbiology and Center for RNA Biology, The Ohio State University, Columbus, Ohio 43210, USA
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10
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Caliskan N, Katunin VI, Belardinelli R, Peske F, Rodnina MV. Programmed -1 frameshifting by kinetic partitioning during impeded translocation. Cell 2014; 157:1619-31. [PMID: 24949973 PMCID: PMC7112342 DOI: 10.1016/j.cell.2014.04.041] [Citation(s) in RCA: 122] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 02/17/2014] [Accepted: 04/10/2014] [Indexed: 02/04/2023]
Abstract
Programmed –1 ribosomal frameshifting (−1PRF) is an mRNA recoding event utilized by cells to enhance the information content of the genome and to regulate gene expression. The mechanism of –1PRF and its timing during translation elongation are unclear. Here, we identified the steps that govern –1PRF by following the stepwise movement of the ribosome through the frameshifting site of a model mRNA derived from the IBV 1a/1b gene in a reconstituted in vitro translation system from Escherichia coli. Frameshifting occurs at a late stage of translocation when the two tRNAs are bound to adjacent slippery sequence codons of the mRNA. The downstream pseudoknot in the mRNA impairs the closing movement of the 30S subunit head, the dissociation of EF-G, and the release of tRNA from the ribosome. The slippage of the ribosome into the –1 frame accelerates the completion of translocation, thereby further favoring translation in the new reading frame. Kinetics of –1 ribosomal frameshifting are monitored at single-codon resolution Frameshifting occurs when the backward movement of the 30S subunit head is impeded Two tRNAs at the XXXYYYZ mRNA sequence are stalled in chimeric POST states The shift to the –1 reading frame occurs prior to EF-G release from the ribosome
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Affiliation(s)
- Neva Caliskan
- Max Planck Institute for Biophysical Chemistry, Department of Physical Biochemistry, 37077 Göttingen, Germany
| | - Vladimir I Katunin
- B.P. Konstantinov Petersburg Nuclear Physics Institute, Department of Molecular and Radiation Biophysics, 188300 Gatchina, Russia
| | - Riccardo Belardinelli
- Max Planck Institute for Biophysical Chemistry, Department of Physical Biochemistry, 37077 Göttingen, Germany
| | - Frank Peske
- Max Planck Institute for Biophysical Chemistry, Department of Physical Biochemistry, 37077 Göttingen, Germany
| | - Marina V Rodnina
- Max Planck Institute for Biophysical Chemistry, Department of Physical Biochemistry, 37077 Göttingen, Germany.
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11
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Holtkamp W, Wintermeyer W, Rodnina MV. Synchronous tRNA movements during translocation on the ribosome are orchestrated by elongation factor G and GTP hydrolysis. Bioessays 2014; 36:908-18. [PMID: 25118068 DOI: 10.1002/bies.201400076] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The translocation of tRNAs through the ribosome proceeds through numerous small steps in which tRNAs gradually shift their positions on the small and large ribosomal subunits. The most urgent questions are: (i) whether these intermediates are important; (ii) how the ribosomal translocase, the GTPase elongation factor G (EF-G), promotes directed movement; and (iii) how the energy of GTP hydrolysis is coupled to movement. In the light of recent advances in biophysical and structural studies, we argue that intermediate states of translocation are snapshots of dynamic fluctuations that guide the movement. In contrast to current models of stepwise translocation, kinetic evidence shows that the tRNAs move synchronously on the two ribosomal subunits in a rapid reaction orchestrated by EF-G and GTP hydrolysis. EF-G combines the energy regimes of a GTPase and a motor protein and facilitates tRNA movement by a combination of directed Brownian ratchet and power stroke mechanisms.
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Affiliation(s)
- Wolf Holtkamp
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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12
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Ren Q, Au HHT, Wang QS, Lee S, Jan E. Structural determinants of an internal ribosome entry site that direct translational reading frame selection. Nucleic Acids Res 2014; 42:9366-82. [PMID: 25038250 PMCID: PMC4132737 DOI: 10.1093/nar/gku622] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The dicistrovirus intergenic internal ribosome entry site (IGR IRES) directly recruits the ribosome and initiates translation using a non-AUG codon. A subset of IGR IRESs initiates translation in either of two overlapping open reading frames (ORFs), resulting in expression of the 0 frame viral structural polyprotein and an overlapping +1 frame ORFx. A U–G base pair adjacent to the anticodon-like pseudoknot of the IRES directs +1 frame translation. Here, we show that the U-G base pair is not absolutely required for +1 frame translation. Extensive mutagenesis demonstrates that 0 and +1 frame translation can be uncoupled. Ribonucleic acid (RNA) structural probing analyses reveal that the mutant IRESs adopt distinct conformations. Toeprinting analysis suggests that the reading frame is selected at a step downstream of ribosome assembly. We propose a model whereby the IRES adopts conformations to occlude the 0 frame aminoacyl-tRNA thereby allowing delivery of the +1 frame aminoacyl-tRNA to the A site to initiate translation of ORFx. This study provides a new paradigm for programmed recoding mechanisms that increase the coding capacity of a viral genome.
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Affiliation(s)
- Qian Ren
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Hilda H T Au
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Qing S Wang
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Seonghoon Lee
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Eric Jan
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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13
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Dynamics of forward and backward translocation of mRNA in the ribosome. PLoS One 2013; 8:e70789. [PMID: 23951009 PMCID: PMC3739767 DOI: 10.1371/journal.pone.0070789] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Accepted: 06/24/2013] [Indexed: 11/19/2022] Open
Abstract
Translocation of the mRNA-tRNA complex in the ribosome, which is catalyzed by elongation factor EF-G, is one of critical steps in the elongation cycle of protein synthesis. Besides this conventional forward translocation, the backward translocation can also occur, which can be catalyzed by elongation factor LepA. However, the molecular mechanism of the translocation remains elusive. To understand the mechanism, here we study theoretically the dynamics of the forward translocation under various nucleotide states of EF-G and the backward translocation in the absence of and in the presence of LepA. We present a consistent explanation of spontaneous forward translocations in the absence of EF-G, the EF-G-catalyzed forward translocations in the presence of a non-hydrolysable GTP analogue and in the presence of GTP, and the spontaneous and LepA-catalyzed backward translocation. The theoretical results provide quantitative explanations of a lot of different, independent experimental data, and also provide testable predictions.
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14
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Skabkin MA, Skabkina OV, Hellen CUT, Pestova TV. Reinitiation and other unconventional posttermination events during eukaryotic translation. Mol Cell 2013; 51:249-64. [PMID: 23810859 DOI: 10.1016/j.molcel.2013.05.026] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 05/03/2013] [Accepted: 05/23/2013] [Indexed: 02/05/2023]
Abstract
During ribosome recycling, posttermination complexes are dissociated by ABCE1 and eRF1 into 60S and tRNA/mRNA-associated 40S subunits, after which tRNA and mRNA are released by eIF1/eIF1A, Ligatin, or MCT-1/DENR. Occasionally, 40S subunits remain associated with mRNA and reinitiate at nearby AUGs. We recapitulated reinitiation using a reconstituted mammalian translation system. The presence of eIF2, eIF3, eIF1, eIF1A, and Met-tRNAi(Met) was sufficient for recycled 40S subunits to remain on mRNA, scan bidirectionally, and reinitiate at upstream and downstream AUGs if mRNA regions flanking the stop codon were unstructured. Imposition of 3' directionality additionally required eIF4F. Strikingly, posttermination ribosomes were not stably anchored on mRNA and migrated bidirectionally to codons cognate to the P site tRNA. Migration depended on the mode of peptide release (puromycin > eRF1⋅eRF3) and nature of tRNA and was enhanced by eEF2. The mobility of posttermination ribosomes suggests that some reinitiation events could involve 80S ribosomes rather than 40S subunits.
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Affiliation(s)
- Maxim A Skabkin
- Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
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15
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Bullwinkle TJ, Zou SB, Rajkovic A, Hersch SJ, Elgamal S, Robinson N, Smil D, Bolshan Y, Navarre WW, Ibba M. (R)-β-lysine-modified elongation factor P functions in translation elongation. J Biol Chem 2012; 288:4416-23. [PMID: 23277358 DOI: 10.1074/jbc.m112.438879] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Post-translational modification of bacterial elongation factor P (EF-P) with (R)-β-lysine at a conserved lysine residue activates the protein in vivo and increases puromycin reactivity of the ribosome in vitro. The additional hydroxylation of EF-P at the same lysine residue by the YfcM protein has also recently been described. The roles of modified and unmodified EF-P during different steps in translation, and how this correlates to its physiological role in the cell, have recently been linked to the synthesis of polyproline stretches in proteins. Polysome analysis indicated that EF-P functions in translation elongation, rather than initiation as proposed previously. This was further supported by the inability of EF-P to enhance the rate of formation of fMet-Lys or fMet-Phe, indicating that the role of EF-P is not to specifically stimulate formation of the first peptide bond. Investigation of hydroxyl-(β)-lysyl-EF-P showed 30% increased puromycin reactivity but no differences in dipeptide synthesis rates when compared with the β-lysylated form. Unlike disruption of the other genes required for EF-P modification, deletion of yfcM had no phenotypic consequences in Salmonella. Taken together, our findings indicate that EF-P functions in translation elongation, a role critically dependent on post-translational β-lysylation but not hydroxylation.
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Affiliation(s)
- Tammy J Bullwinkle
- Department of Microbiology, Ohio State University, Columbus, Ohio 43210, USA
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16
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Liu Q, Fredrick K. Contribution of intersubunit bridges to the energy barrier of ribosomal translocation. Nucleic Acids Res 2012; 41:565-74. [PMID: 23161696 PMCID: PMC3592451 DOI: 10.1093/nar/gks1074] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
In every round of translation elongation, EF-G catalyzes translocation, the movement of tRNAs (and paired codons) to their adjacent binding sites in the ribosome. Previous kinetic studies have shown that the rate of tRNA–mRNA movement is limited by a conformational change in the ribosome termed ‘unlocking’. Although structural studies offer some clues as to what unlocking might entail, the molecular basis of this conformational change remains an open question. In this study, the contribution of intersubunit bridges to the energy barrier of translocation was systematically investigated. Unlike those targeting B2a and B3, mutations that disrupt bridges B1a, B4, B7a and B8 increased the maximal rate of both forward (EF-G dependent) and reverse (spontaneous) translocation. As bridge B1a is predicted to constrain 30S head movement and B4, B7a and B8 are predicted to constrain intersubunit rotation, these data provide evidence that formation of the unlocked (transition) state involves both 30S head movement and intersubunit rotation.
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Affiliation(s)
- Qi Liu
- Ohio State Biochemistry Program, Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA
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17
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Devaraj A, Fredrick K. Short spacing between the Shine-Dalgarno sequence and P codon destabilizes codon-anticodon pairing in the P site to promote +1 programmed frameshifting. Mol Microbiol 2010; 78:1500-9. [PMID: 21143320 DOI: 10.1111/j.1365-2958.2010.07421.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Programmed frameshifting in the RF2 gene (prfB) involves an intragenic Shine-Dalgarno (SD) sequence. To investigate the role of SD-ASD pairing in the mechanism of frameshifting, we have analysed the effect of spacing between the SD sequence and P codon on P-site tRNA binding and RF2-dependent termination. When the spacing between an extended SD sequence and the P codon is decreased from 4 to 1 nucleotide (nt), the dissociation rate (k(off) ) for P-site tRNA increases by > 100-fold. Toeprinting analysis shows that pre-translocation complexes cannot be formed when the spacer sequence is ≤ 2 nt. Instead, the tRNA added secondarily to fill the A site and its corresponding codon move spontaneously into the P site, resulting in a complex with a 3 nt longer spacer between the SD-ASD helix and the P codon. While close proximity of the SD clearly destabilizes P-site tRNA, RF2-dependent termination and EF-Tu-dependent decoding are largely unaffected in analogous complexes. These data support a model in which formation of the SD-ASD helix in ribosomes stalled at the in-frame UGA codon of prfB generates tension on the mRNA that destabilizes codon-anticodon pairing in the P site and promotes slippage of the mRNA in the 5' direction.
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Affiliation(s)
- Aishwarya Devaraj
- Ohio State Biochemistry Program Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
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18
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Leshin JA, Rakauskaitė R, Dinman JD, Meskauskas A. Enhanced purity, activity and structural integrity of yeast ribosomes purified using a general chromatographic method. RNA Biol 2010; 7:354-60. [PMID: 20404492 DOI: 10.4161/rna.7.3.11648] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
One of the major challenges facing researchers working with eukaryotic ribosomes lies in their lability relative to their eubacterial and archael counterparts. In particular, lysis of cells and purification of eukaryotic ribosomes by conventional differential ultracentrifugation methods exposes them for long periods of time to a wide range of co-purifying proteases and nucleases, negatively impacting their structural integrity and functionality. A chromatographic method using a cysteine charged Sulfolink resin was adapted to address these problems. This fast and simple method significantly reduces co-purifying proteolytic and nucleolytic activities, producing good yields of highly biochemically active yeast ribosomes with fewer nicks in their rRNAs. In particular, the chromatographic purification protocol significantly improved the quality of ribosomes isolated from mutant cells. This method is likely applicable to mammalian ribosomes as well. The simplicity of the method, and the enhanced purity and activity of chromatographically purified ribosome represents a significant technical advancement for the study of eukaryotic ribosomes.
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Affiliation(s)
- Jonathan A Leshin
- Department of Cell Biology & Molecular Genetics, University of Maryland, College Park, MD, USA
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19
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Atkins JF, Gesteland RF, Pennell S. Pseudoknot-Dependent Programmed —1 Ribosomal Frameshifting: Structures, Mechanisms and Models. RECODING: EXPANSION OF DECODING RULES ENRICHES GENE EXPRESSION 2009; 24. [PMCID: PMC7119991 DOI: 10.1007/978-0-387-89382-2_7] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Programmed —1 ribosomal frameshifting is a translational recoding strategy that takes place during the elongation phase of protein biosynthesis. Frameshifting occurs in response to specific signals in the mRNA; a slippery sequence, where the ribosome changes frame, and a stimulatory RNA secondary structure, usually a pseudoknot, located immediately downstream. During the frameshift the ribosome slips backwards by a single nucleotide (in the 5′-wards/—1 direction) and continues translation in the new, overlapping reading frame, generating a fusion protein composed of the products of both the original and the —1 frame coding regions. In eukaryotes, frameshifting is largely a phenomenon of virus gene expression and associated predominantly with the expression of viral replicases. Research on frameshifting impacts upon diverse topics, including the ribosomal elongation cycle, RNA structure and function, tRNA modification, virus replication, antiviral intervention, evolution and bioinformatics. This chapter focuses on the structure and function of frameshift-stimulatory RNA pseudoknots and mechanistic aspects of ribosomal frameshifting. A variety of models of the frameshifting process are discussed in the light of recent advances in our understanding of ribosome structure and the elongation cycle.
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Affiliation(s)
- John F. Atkins
- grid.223827.e0000000121930096Molecular Biology Program, University of Utah, N. 2030 E. 15, Salt Late City, 84112-5330 U.S.A.
| | - Raymond F. Gesteland
- grid.223827.e0000000121930096Dept. Bioengineering, University of Utah, Salt Lake City, 84112 U.S.A.
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20
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Shoji S, Abdi NM, Bundschuh R, Fredrick K. Contribution of ribosomal residues to P-site tRNA binding. Nucleic Acids Res 2009; 37:4033-42. [PMID: 19417061 PMCID: PMC2709574 DOI: 10.1093/nar/gkp296] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Structural studies have revealed multiple contacts between the ribosomal P site and tRNA, but how these contacts contribute to P-tRNA binding remains unclear. In this study, the effects of ribosomal mutations on the dissociation rate (k(off)) of various tRNAs from the P site were measured. Mutation of the 30S P site destabilized tRNAs to various degrees, depending on the mutation and the species of tRNA. These data support the idea that ribosome-tRNA interactions are idiosyncratically tuned to ensure stable binding of all tRNA species. Unlike deacylated elongator tRNAs, N-acetyl-aminoacyl-tRNAs and tRNA(fMet) dissociated from the P site at a similar low rate, even in the presence of various P-site mutations. These data provide evidence for a stability threshold for P-tRNA binding and suggest that ribosome-tRNA(fMet) interactions are uniquely tuned for tight binding. The effects of 16S rRNA mutation G1338U were suppressed by 50S E-site mutation C2394A, suggesting that G1338 is particularly important for stabilizing tRNA in the P/E site. Finally, mutation C2394A or the presence of an N-acetyl-aminoacyl group slowed the association rate (k(on)) of tRNA dramatically, suggesting that deacylated tRNA binds the P site of the ribosome via the E site.
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Affiliation(s)
- Shinichiro Shoji
- Department of Microbiology, The Ohio State University, 484 W., 12th Ave, Columbus, OH 43210, USA
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21
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Jang CJ, Lo MCY, Jan E. Conserved element of the dicistrovirus IGR IRES that mimics an E-site tRNA/ribosome interaction mediates multiple functions. J Mol Biol 2009; 387:42-58. [PMID: 19361441 DOI: 10.1016/j.jmb.2009.01.042] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Revised: 01/20/2009] [Accepted: 01/21/2009] [Indexed: 02/05/2023]
Abstract
The internal ribosome entry site within the intergenic region (IGR IRES) of the Dicistroviridae family mimics a tRNA to directly assemble 80 S ribosomes and initiate translation at a non-AUG codon from the ribosomal A-site. A comparison of IGR IRESs within this viral family reveals structural similarity but little sequence similarity. However, a few specific conserved elements exist, which likely have important roles in IRES function. In this study, we have generated a battery of mutations to characterize the role of a conserved loop (L1.1) region of the IGR IRES. Mutating specific nucleotides within the L1.1 region inhibited IGR IRES-mediated translation in rabbit reticulocyte lysates. By assaying different steps in IRES function, we found that the mutant L1.1 IRESs had reduced affinity for 80 S ribosomes but not 40 S subunits, indicating that the L1.1 region mediated either binding to preformed 80 S or 60 S joining. Furthermore, mutations in L1.1 altered the position of the ribosome on the mutant IRES, indicating that the tRNA-like anticodon/codon mimic within the ribosomal P-site is disrupted. Structural studies have revealed that the L1.1 region interacts with the L1 stalk of the 60 S subunit, which is similar to the interactions between the T-loop of the E-site tRNA and ribosomal protein rpL1. Our results demonstrate that the conserved L1.1 region directs multiple steps in IGR IRES-mediated translation including ribosome binding and positioning, which are functions that the E-site tRNA may normally mediate during translation.
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Affiliation(s)
- Christopher J Jang
- Department of Biochemistry and Molecular Biology, University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, Canada
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22
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Agirrezabala X, Lei J, Brunelle JL, Ortiz-Meoz RF, Green R, Frank J. Visualization of the hybrid state of tRNA binding promoted by spontaneous ratcheting of the ribosome. Mol Cell 2008; 32:190-7. [PMID: 18951087 DOI: 10.1016/j.molcel.2008.10.001] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Revised: 08/12/2008] [Accepted: 10/01/2008] [Indexed: 10/21/2022]
Abstract
A crucial step in translation is the translocation of tRNAs through the ribosome. In the transition from one canonical site to the other, the tRNAs acquire intermediate configurations, so-called hybrid states. At this stage, the small subunit is rotated with respect to the large subunit, and the anticodon stem loops reside in the A and P sites of the small subunit, while the acceptor ends interact with the P and E sites of the large subunit. In this work, by means of cryo-EM and particle classification procedures, we visualize the hybrid state of both A/P and P/E tRNAs in an authentic factor-free ribosome complex during translocation. In addition, we show how the repositioning of the tRNAs goes hand in hand with the change in the interplay between S13, L1 stalk, L5, H68, H69, and H38 that is caused by the ratcheting of the small subunit.
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Affiliation(s)
- Xabier Agirrezabala
- Howard Hughes Medical Institute, Columbia University, 630 West 168th Street, College of Physicians and Surgeons, Black Building 2-221, New York, NY 10032, USA
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23
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Abstract
Programmed ribosomal frameshifting (PRF) is one of the multiple translational recoding processes that fundamentally alters triplet decoding of the messenger RNA by the elongating ribosome. The ability of the ribosome to change translational reading frames in the −1 direction (−1 PRF) is employed by many positive strand RNA viruses, including economically important plant viruses and many human pathogens, such as retroviruses, e.g., HIV-1, and coronaviruses, e.g., the causative agent of severe acute respiratory syndrome (SARS), in order to properly express their genomes. −1 PRF is programmed by a bipartite signal embedded in the mRNA and includes a heptanucleotide “slip site” over which the paused ribosome “backs up” by one nucleotide, and a downstream stimulatory element, either an RNA pseudoknot or a very stable RNA stem–loop. These two elements are separated by six to eight nucleotides, a distance that places the 5′ edge of the downstream stimulatory element in direct contact with the mRNA entry channel of the 30S ribosomal subunit. The precise mechanism by which the downstream RNA stimulates −1 PRF by the translocating ribosome remains unclear. This review summarizes the recent structural and biophysical studies of RNA pseudoknots and places this work in the context of our evolving mechanistic understanding of translation elongation. Support for the hypothesis that the downstream stimulatory element provides a kinetic barrier to the ribosome-mediated unfolding is discussed.
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24
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Abstract
During translation, tRNAs must move rapidly to their adjacent sites in the ribosome while maintaining precise pairing with mRNA. This movement (translocation) occurs in a stepwise manner with hybrid-state intermediates, but it is unclear how these hybrid states relate to kinetically defined events of translocation. Here we analyze mutations at position 2394 of 23S rRNA in a pre-steady-state kinetic analysis of translocation. These mutations target the 50S E site and are predicted to inhibit P/E state formation. Each mutation decreases growth rate, the maximal rate of translocation (k(trans)), and the apparent affinity of EF-G for the pretranslocation complex (i.e., increases K(1/2)). The magnitude of these defects follows the trend A > G > U. Because the C2394A mutation did not decrease the rate of single-turnover GTP hydrolysis, the >20-fold increase in K(1/2) conferred by C2394A can be attributed to neither the initial binding of EF-G nor the subsequent GTP hydrolysis step. We propose that C2394A inhibits a later step, P/E state formation, to confer its effects on translocation. Replacement of the peptidyl group with an aminoacyl group, which is predicted to inhibit A/P state formation, decreases k(trans) without increasing K(1/2). These data suggest that movements of tRNA into the P/E and A/P sites are separable events. This mutational study allows tRNA movements with respect to both subunits to be integrated into a kinetic model for translocation.
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25
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Walker SE, Fredrick K. Preparation and evaluation of acylated tRNAs. Methods 2008; 44:81-6. [PMID: 18241790 DOI: 10.1016/j.ymeth.2007.09.003] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 09/17/2007] [Accepted: 09/18/2007] [Indexed: 10/22/2022] Open
Abstract
In the cell, the activity of tRNA is governed by its acylation state. Interactions with the ribosome, translation factors, and regulatory elements are strongly influenced by the acyl group, and presumably other cellular components that interact with tRNA also use the acyl group as a specificity determinant. Thus, those using biochemical approaches to study any aspect of tRNA biology should be familiar with effective methods to prepare and evaluate acylated tRNA reagents. Here, methods to prepare aminoacyl-tRNA, N-acetyl-aminoacyl-tRNA, and fMet-tRNA(fMet) and to assess their homogeneity are described. Using these methods, acylated tRNAs of high homogeneity can be reliably obtained.
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Affiliation(s)
- Sarah E Walker
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
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26
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tRNA-mRNA mimicry drives translation initiation from a viral IRES. Nat Struct Mol Biol 2007; 15:57-64. [PMID: 18157151 DOI: 10.1038/nsmb1351] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2007] [Accepted: 11/16/2007] [Indexed: 01/02/2023]
Abstract
Internal ribosome entry site (IRES) RNAs initiate protein synthesis in eukaryotic cells by a noncanonical cap-independent mechanism. IRESes are critical for many pathogenic viruses, but efforts to understand their function are complicated by the diversity of IRES sequences as well as by limited high-resolution structural information. The intergenic region (IGR) IRESes of the Dicistroviridae viruses are powerful model systems to begin to understand IRES function. Here we present the crystal structure of a Dicistroviridae IGR IRES domain that interacts with the ribosome's decoding groove. We find that this RNA domain precisely mimics the transfer RNA anticodon-messenger RNA codon interaction, and its modeled orientation on the ribosome helps explain translocation without peptide bond formation. When combined with a previous structure, this work completes the first high-resolution description of an IRES RNA and provides insight into how RNAs can manipulate complex biological machines.
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27
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Li W, Frank J. Transfer RNA in the hybrid P/E state: correlating molecular dynamics simulations with cryo-EM data. Proc Natl Acad Sci U S A 2007; 104:16540-5. [PMID: 17925437 PMCID: PMC2034235 DOI: 10.1073/pnas.0708094104] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Indexed: 11/18/2022] Open
Abstract
Transfer RNA (tRNA) transiently occupies the hybrid P/E state (P/E-tRNA) when mRNA-tRNA are translocated in the ribosome. In this study, we characterize the structure of P/E-tRNA and its interactions with the ribosome by correlating the results from molecular dynamics simulations on free tRNA with the cryo-EM map of P/E-tRNA. In our approach, we show that the cryo-EM map may be interpreted as a conformational average. Along the molecular dynamics trajectories (44 ns, 18 ns, and 18 ns), some of the snapshots prove to be quite close to the observed density. In a representative structure, the CCA (3') arm is uniquely twisted, and the anticodon stem loop is kinked at the junctions to both the anticodon loop and the D stem. In addition, the map shows that the P/E-tRNA is no longer bound to helix H69 of 23S rRNA and is flexible, and the conformations of helices H68 and h44 of 16S rRNA differ from those in the x-ray structure. Thus, our study presents structural and dynamic information on the P/E-tRNA and characterizes its interactions with the translocating ribosome.
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Affiliation(s)
- Wen Li
- *Wadsworth Center, Empire State Plaza, Albany, NY 12201-0509
| | - Joachim Frank
- *Wadsworth Center, Empire State Plaza, Albany, NY 12201-0509
- Howard Hughes Medical Institute, Health Research, Inc., Wadsworth Center, Empire State Plaza, Albany, NY 12201-0509; and
- Department of Biomedical Sciences, University at Albany, State University of New York, Wadsworth Center, Empire State Plaza, Albany, NY 12201-0509
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28
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Spiegel PC, Ermolenko DN, Noller HF. Elongation factor G stabilizes the hybrid-state conformation of the 70S ribosome. RNA (NEW YORK, N.Y.) 2007; 13:1473-82. [PMID: 17630323 PMCID: PMC1950763 DOI: 10.1261/rna.601507] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Following peptide bond formation, transfer RNAs (tRNAs) and messenger RNA (mRNA) are translocated through the ribosome, a process catalyzed by elongation factor EF-G. Here, we have used a combination of chemical footprinting, peptidyl transferase activity assays, and mRNA toeprinting to monitor the effects of EF-G on the positions of tRNA and mRNA relative to the A, P, and E sites of the ribosome in the presence of GTP, GDP, GDPNP, and fusidic acid. Chemical footprinting experiments show that binding of EF-G in the presence of the non-hydrolyzable GTP analog GDPNP or GDP.fusidic acid induces movement of a deacylated tRNA from the classical P/P state to the hybrid P/E state. Furthermore, stabilization of the hybrid P/E state by EF-G compromises P-site codon-anticodon interaction, causing frame-shifting. A deacylated tRNA bound to the P site and a peptidyl-tRNA in the A site are completely translocated to the E and P sites, respectively, in the presence of EF-G with GTP or GDPNP but not with EF-G.GDP. Unexpectedly, translocation with EF-G.GTP leads to dissociation of deacylated tRNA from the E site, while tRNA remains bound in the presence of EF-G.GDPNP, suggesting that dissociation of tRNA from the E site is promoted by GTP hydrolysis and/or EF-G release. Our results show that binding of EF-G in the presence of GDPNP or GDP.fusidic acid stabilizes the ribosomal intermediate hybrid state, but that complete translocation is supported only by EF-G.GTP or EF-G.GDPNP.
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Affiliation(s)
- P Clint Spiegel
- Center for Molecular Biology of RNA, Department of Molecular, Cell and Developmental Biology, University of California-Santa Cruz 95064, USA
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29
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Abstract
The ribosome is responsible for protein synthesis, the translation of the genetic code, in all living organisms. Ribosomes are composed of RNA (ribosomal RNA) and protein (ribosomal protein). Soluble protein factors bind to the ribosome and facilitate different phases of translation. Genetic approaches have proved useful for the identification and characterization of the structural and functional roles of specific nucleotides in ribosomal RNA and of specific amino acids in ribosomal proteins and in ribosomal factors. This chapter summarizes examples of mutations identified in ribosomal RNA, ribosomal proteins, and ribosomal factors.
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MESH Headings
- Animals
- Base Sequence
- DNA Mutational Analysis
- Humans
- Mutation
- Nucleic Acid Conformation
- Peptide Elongation Factors/genetics
- Peptide Initiation Factors/genetics
- Peptide Termination Factors/genetics
- Protein Subunits/genetics
- RNA, Ribosomal, 16S/analysis
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/physiology
- RNA, Ribosomal, 23S/analysis
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/physiology
- Ribosomal Proteins/genetics
- Ribosomes/genetics
- Sequence Analysis, RNA
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Affiliation(s)
- Kathleen L Triman
- Department of Biology, Franklin and Marshall College, Lancaster, PA 17604, USA
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30
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Shoji S, Walker SE, Fredrick K. Reverse translocation of tRNA in the ribosome. Mol Cell 2006; 24:931-42. [PMID: 17189194 PMCID: PMC2661759 DOI: 10.1016/j.molcel.2006.11.025] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 10/18/2006] [Accepted: 11/29/2006] [Indexed: 11/24/2022]
Abstract
A widely held view is that directional movement of tRNA in the ribosome is determined by an intrinsic mechanism and driven thermodynamically by transpeptidation. Here, we show that, in certain ribosomal complexes, the pretranslocation (PRE) state is thermodynamically favored over the posttranslocation (POST) state. Spontaneous and efficient conversion from the POST to PRE state is observed when EF-G is depleted from ribosomes in the POST state or when tRNA is added to the E site of ribosomes containing P-site tRNA. In the latter assay, the rate of tRNA movement is increased by streptomycin and neomycin, decreased by tetracycline, and not affected by the acylation state of the tRNA. In one case, we provide evidence that complex conversion occurs by reverse translocation (i.e., direct movement of the tRNAs from the E and P sites to the P and A sites, respectively). These findings have important implications for the energetics of translocation.
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Affiliation(s)
- Shinichiro Shoji
- Department of Microbiology, The Ohio State University, Columbus, Ohio 43210
| | - Sarah E. Walker
- Department of Microbiology, The Ohio State University, Columbus, Ohio 43210
| | - Kurt Fredrick
- Department of Microbiology, The Ohio State University, Columbus, Ohio 43210
- Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio 43210
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31
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Berk V, Zhang W, Pai RD, Cate JHD. Structural basis for mRNA and tRNA positioning on the ribosome. Proc Natl Acad Sci U S A 2006; 103:15830-4. [PMID: 17038497 PMCID: PMC1635088 DOI: 10.1073/pnas.0607541103] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Indexed: 12/23/2022] Open
Abstract
Protein synthesis requires the accurate positioning of mRNA and tRNA in the peptidyl-tRNA site of the ribosome. Here we describe x-ray crystal structures of the intact bacterial ribosome from Escherichia coli in a complex with mRNA and the anticodon stem-loop of P-site tRNA. At 3.5-A resolution, these structures reveal rearrangements in the intact ribosome that clamp P-site tRNA and mRNA on the small ribosomal subunit. Binding of the anticodon stem-loop of P-site tRNA to the ribosome is sufficient to lock the head of the small ribosomal subunit in a single conformation, thereby preventing movement of mRNA and tRNA before mRNA decoding.
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Affiliation(s)
- Veysel Berk
- Departments of *Molecular and Cell Biology, and
| | - Wen Zhang
- Chemistry, University of California, Berkeley, CA 94720; and
| | - Raj D. Pai
- Departments of *Molecular and Cell Biology, and
| | - Jamie H. D. Cate
- Departments of *Molecular and Cell Biology, and
- Chemistry, University of California, Berkeley, CA 94720; and
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
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32
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Korostelev A, Trakhanov S, Laurberg M, Noller HF. Crystal Structure of a 70S Ribosome-tRNA Complex Reveals Functional Interactions and Rearrangements. Cell 2006; 126:1065-77. [PMID: 16962654 DOI: 10.1016/j.cell.2006.08.032] [Citation(s) in RCA: 382] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 08/10/2006] [Accepted: 08/30/2006] [Indexed: 11/16/2022]
Abstract
Our understanding of the mechanism of protein synthesis has undergone rapid progress in recent years as a result of low-resolution X-ray and cryo-EM structures of ribosome functional complexes and high-resolution structures of ribosomal subunits and vacant ribosomes. Here, we present the crystal structure of the Thermus thermophilus 70S ribosome containing a model mRNA and two tRNAs at 3.7 A resolution. Many structural details of the interactions between the ribosome, tRNA, and mRNA in the P and E sites and the ways in which tRNA structure is distorted by its interactions with the ribosome are seen. Differences between the conformations of vacant and tRNA-bound 70S ribosomes suggest an induced fit of the ribosome structure in response to tRNA binding, including significant changes in the peptidyl-transferase catalytic site.
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Affiliation(s)
- Andrei Korostelev
- Center for Molecular Biology of RNA and Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, CA 95064, USA
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Walker SE, Fredrick K. Recognition and positioning of mRNA in the ribosome by tRNAs with expanded anticodons. J Mol Biol 2006; 360:599-609. [PMID: 16730356 PMCID: PMC2602952 DOI: 10.1016/j.jmb.2006.05.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2006] [Revised: 04/28/2006] [Accepted: 05/01/2006] [Indexed: 10/24/2022]
Abstract
Mutant tRNAs containing an extra nucleotide in the anticodon loop are known to suppress +1 frameshift mutations, but in no case has the molecular mechanism been clarified. It has been proposed that the expanded anticodon pairs with a complementary mRNA sequence (the frameshift sequence) in the A site, and this quadruplet "codon-anticodon" helix is translocated to the P site to restore the correct reading frame. Here, we analyze the ability of tRNA analogs containing expanded anticodons to recognize and position mRNA in ribosomal complexes in vitro. In all cases tested, 8 nt anticodon loops position the 3' three-quarters of the frameshift sequence in the P site, indicating that the 5' bases of the expanded anticodon (nucleotides 33.5, 34, and 35) pair with mRNA in the P site. We also provide evidence that four base-pairs can form between the P-site tRNA and mRNA, and the fourth base-pair involves nucleotide 36 of the tRNA and lies toward (or in) the 30 S E site. In the A site, tRNA analogs with the expanded anticodon ACCG are able to recognize either CGG or GGU. These data imply a flexibility of the expanded anticodon in the A site. Recognition of the 5' three-quarters of the frameshift sequence in the A site and subsequent translocation of the expanded anticodon to the P site results in movement of mRNA by four nucleotides, explaining how these tRNAs can change the mRNA register in the ribosome to restore the correct reading frame.
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Affiliation(s)
- Sarah E. Walker
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
| | - Kurt Fredrick
- Department of Microbiology, The Ohio State University, Columbus, OH 43210, USA
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210, USA
- Corresponding author E-mail address of the corresponding author:
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