1
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Ali Z, Kukhta T, Trant JF, Sharma P. An Atlas of the base inter-RNA stacks involved in bacterial translation. Biophys Chem 2024; 305:107144. [PMID: 38061282 DOI: 10.1016/j.bpc.2023.107144] [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: 11/01/2023] [Accepted: 11/28/2023] [Indexed: 01/03/2024]
Abstract
Nucleobase-specific noncovalent interactions play a crucial role in translation. Herein, we provide a comprehensive analysis of the stacks between different RNA components in the crystal structures of the bacterial ribosome caught at different translation stages. Analysis of tRNA||rRNA stacks reveals distinct behaviour; both the A-and E-site tRNAs exhibit unique stacking patterns with 23S rRNA bases, while P-site tRNAs stack with 16S rRNA bases. Furthermore, E-site stacks exhibit diverse face orientations and ring topologies-rare for inter-chain RNA interactions-with higher average interaction energies than A or P-site stacks. This suggests that stacking may be essential for stabilizing tRNA progression through the E-site. Additionally, mRNA||rRNA stacks reveal other geometries, which depend on the tRNA binding site, whereas 16S rRNA||23S rRNA stacks highlight the importance of specific bases in maintaining the integrity of the translational complex by linking the two rRNAs. Furthermore, tRNA||mRNA stacks exhibit distinct geometries and energetics at the E-site, indicating their significance during tRNA translocation and elimination. Overall, both A and E-sites display a more diverse distribution of inter-RNA stacks compared to the P-site. Stacking interactions in the active ribosome are not simply accidental byproducts of biochemistry but are likely invoked to compensate and support the integrity and dynamics of translation.
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MESH Headings
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/genetics
- RNA, Ribosomal, 16S/metabolism
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/genetics
- RNA, Ribosomal, 23S/metabolism
- Ribosomes/chemistry
- RNA, Transfer/chemistry
- RNA, Transfer/genetics
- RNA, Transfer/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/analysis
- RNA, Messenger/metabolism
- Nucleic Acid Conformation
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Affiliation(s)
- Zakir Ali
- Computational Biochemistry Laboratory, Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India
| | - Teagan Kukhta
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Ave., Windsor, ON N9B 3P4, Canada
| | - John F Trant
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Ave., Windsor, ON N9B 3P4, Canada; We-Spark Health Institute, 401 Sunset Ave., Windsor, ON N9B 3P4, Canada; Binary Star Research Services, LaSalle, ON N9J 3X8, Canada.
| | - Purshotam Sharma
- Computational Biochemistry Laboratory, Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India; Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Ave., Windsor, ON N9B 3P4, Canada.
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2
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Kwon I, Choi ES. Forced Ambiguity of the Leucine Codons for Multiple-Site-Specific Incorporation of a Noncanonical Amino Acid. PLoS One 2016; 11:e0152826. [PMID: 27028506 PMCID: PMC4814082 DOI: 10.1371/journal.pone.0152826] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 03/03/2016] [Indexed: 11/24/2022] Open
Abstract
Multiple-site-specific incorporation of a noncanonical amino acid into a recombinant protein would be a very useful technique to generate multiple chemical handles for bioconjugation and multivalent binding sites for the enhanced interaction. Previously combination of a mutant yeast phenylalanyl-tRNA synthetase variant and the yeast phenylalanyl-tRNA containing the AAA anticodon was used to incorporate a noncanonical amino acid into multiple UUU phenylalanine (Phe) codons in a site-specific manner. However, due to the less selective codon recognition of the AAA anticodon, there was significant misincorporation of a noncanonical amino acid into unwanted UUC Phe codons. To enhance codon selectivity, we explored degenerate leucine (Leu) codons instead of Phe degenerate codons. Combined use of the mutant yeast phenylalanyl-tRNA containing the CAA anticodon and the yPheRS_naph variant allowed incorporation of a phenylalanine analog, 2-naphthylalanine, into murine dihydrofolate reductase in response to multiple UUG Leu codons, but not to other Leu codon sites. Despite the moderate UUG codon occupancy by 2-naphthylalaine, these results successfully demonstrated that the concept of forced ambiguity of the genetic code can be achieved for the Leu codons, available for multiple-site-specific incorporation.
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Affiliation(s)
- Inchan Kwon
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
- Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia, United States of America
- * E-mail:
| | - Eun Sil Choi
- School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
- Department of Biological Sciences, College of Natural Sciences, Chonnam National University, Gwangju, Republic of Korea
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3
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Večerek B, Moll I, Bläsi U. Control of Fur synthesis by the non-coding RNA RyhB and iron-responsive decoding. EMBO J 2007; 26:965-75. [PMID: 17268550 PMCID: PMC1852835 DOI: 10.1038/sj.emboj.7601553] [Citation(s) in RCA: 139] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Accepted: 12/18/2006] [Indexed: 11/08/2022] Open
Abstract
The Fe2+-dependent Fur protein serves as a negative regulator of iron uptake in bacteria. As only metallo-Fur acts as an autogeneous repressor, Fe2+scarcity would direct fur expression when continued supply is not obviously required. We show that in Escherichia coli post-transcriptional regulatory mechanisms ensure that Fur synthesis remains steady in iron limitation. Our studies revealed that fur translation is coupled to that of an upstream open reading frame (uof), translation of which is downregulated by the non-coding RNA (ncRNA) RyhB. As RyhB transcription is negatively controlled by metallo-Fur, iron depletion creates a negative feedback loop. RyhB-mediated regulation of uof-fur provides the first example for indirect translational regulation by a trans-encoded ncRNA. In addition, we present evidence for an iron-responsive decoding mechanism of the uof-fur entity. It could serve as a backup mechanism of the RyhB circuitry, and represents the first link between iron availability and synthesis of an iron-containing protein.
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Affiliation(s)
- Branislav Večerek
- Department of Microbiology and Immunobiology, Max F Perutz Laboratories, University of Vienna, Vienna, Austria
| | - Isabella Moll
- Department of Microbiology and Immunobiology, Max F Perutz Laboratories, University of Vienna, Vienna, Austria
| | - Udo Bläsi
- Department of Microbiology and Immunobiology, Max F Perutz Laboratories, University of Vienna, Vienna, Austria
- Department of Microbiology and Immunobiology, Max F Perutz Laboratories, University of Vienna, Dr. Bohrgasse 9/4, Vienna 1030, Austria. Tel.: +43 1 4277 54609; Fax: +43 1 4277 9546; E-mail:
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4
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Agris PF, Vendeix FAP, Graham WD. tRNA's wobble decoding of the genome: 40 years of modification. J Mol Biol 2006; 366:1-13. [PMID: 17187822 DOI: 10.1016/j.jmb.2006.11.046] [Citation(s) in RCA: 400] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 11/06/2006] [Accepted: 11/10/2006] [Indexed: 11/20/2022]
Abstract
The genetic code is degenerate, in that 20 amino acids are encoded by 61 triplet codes. In 1966, Francis Crick hypothesized that the cell's limited number of tRNAs decoded the genome by recognizing more than one codon. The ambiguity of that recognition resided in the third base-pair, giving rise to the Wobble Hypothesis. Post-transcriptional modifications at tRNA's wobble position 34, especially modifications of uridine 34, enable wobble to occur. The Modified Wobble Hypothesis proposed in 1991 that specific modifications of a tRNA wobble nucleoside shape the anticodon architecture in such a manner that interactions were restricted to the complementary base plus a single wobble pairing for amino acids with twofold degenerate codons. However, chemically different modifications at position 34 would expand the ability of a tRNA to read three or even four of the fourfold degenerate codons. One foundation of Crick's Wobble Hypothesis was that a near-constant geometry of canonical base-pairing be maintained in forming all three base-pairs between the tRNA anticodon and mRNA codon on the ribosome. In accepting an aminoacyl-tRNA, the ribosome requires maintenance of a specific geometry for the anticodon-codon base-pairing. However, it is the post-transcriptional modifications at tRNA wobble position 34 and purine 37, 3'-adjacent to the anticodon, that pre-structure the anticodon domain to ensure the correct codon binding. The modifications create both the architecture and the stability needed for decoding through restraints on anticodon stereochemistry and conformational space, and through selective hydrogen bonding. A physicochemical understanding of modified nucleoside contributions to the tRNA anticodon domain architecture and its decoding of the genome has advanced RNA world evolutionary theory, the principles of RNA chemistry, and the application of this knowledge to the introduction of new amino acids to proteins.
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Affiliation(s)
- Paul F Agris
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, NC 27695-7622, USA.
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5
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Baranov PV, Gesteland RF, Atkins JF. P-site tRNA is a crucial initiator of ribosomal frameshifting. RNA (NEW YORK, N.Y.) 2004; 10:221-30. [PMID: 14730021 PMCID: PMC1370534 DOI: 10.1261/rna.5122604] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2003] [Accepted: 10/09/2003] [Indexed: 05/22/2023]
Abstract
The expression of some genes requires a high proportion of ribosomes to shift at a specific site into one of the two alternative frames. This utilized frameshifting provides a unique tool for studying reading frame control. Peptidyl-tRNA slippage has been invoked to explain many cases of programmed frameshifting. The present work extends this to other cases. When the A-site is unoccupied, the P-site tRNA can be repositioned forward with respect to mRNA (although repositioning in the minus direction is also possible). A kinetic model is presented for the influence of both, the cognate tRNAs competing for overlapping codons in A-site, and the stabilities of P-site tRNA:mRNA complexes in the initial and new frames. When the A-site is occupied, the P-site tRNA can be repositioned backward. Whether frameshifting will happen depends on the ability of the A-site tRNA to subsequently be repositioned to maintain physical proximity of the tRNAs. This model offers an alternative explanation to previously published mechanisms of programmed frameshifting, such as out-of-frame tRNA binding, and a different perspective on simultaneous tandem tRNA slippage.
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Affiliation(s)
- Pavel V Baranov
- Department of Human Genetics, University of Utah, Salt Lake City, Utah 84112-5330, USA
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6
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Fuglsang A. The effective number of codons for individual amino acids: some codons are more optimal than others. Gene 2004; 320:185-90. [PMID: 14597402 DOI: 10.1016/s0378-1119(03)00829-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The aim of this study was to evaluate the codon bias using the effective number of codons for individual amino acids (N(c)(AA)) and to assess the codon bias in relation to the definition of optimal codons, using Escherichia coli as a model organism. We show that a general correlation exists between the effective number of codons (Ncirc(c)) or codon adaptation index (CAI) and N(c)(AA), but that this correlation is not equally strong for all amino acids within a degeneracy group. For example, leucine codons contribute more to Ncirc(c) and the codon adaptation index than serine codons. A possible explanation is that some optimal codons are more optimal than others, in terms of the selectional advantage they offer. This hypothesis is confirmed by further analysis on the correlations that exist between values for relative synonymous codon usage (RSCU), N(c)(AA), and the codon adaptation index.
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Affiliation(s)
- Anders Fuglsang
- Danish University of Pharmaceutical Sciences, Institute of Pharmacology, Universitetsparken 2, DK-2100, Copenhagen Ø, Denmark.
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7
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Urbonavičius J, Qian Q, Durand JM, Hagervall TG, Björk GR. Improvement of reading frame maintenance is a common function for several tRNA modifications. EMBO J 2001; 20:4863-73. [PMID: 11532950 PMCID: PMC125605 DOI: 10.1093/emboj/20.17.4863] [Citation(s) in RCA: 381] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Transfer RNAs from all organisms contain many modified nucleosides. Their vastly different chemical structures, their presence in different tRNAs, their occurrence in different locations in tRNA and their influence on different reactions in which tRNA participates suggest that each modified nucleoside may have its own specific function. However, since the frequency of frameshifting in several different mutants [mnmA, mnmE, tgt, truA (hisT), trmD, miaA, miaB and miaE] defective in tRNA modification was higher compared with the corresponding wild-type controls, these modifications have a common function: they all improve reading frame maintenance. Frameshifting occurs by peptidyl-tRNA slippage, which is influenced by the hypomodified tRNA in two ways: (i) a hypomodified tRNA in the ternary complex may decrease the rate by which the complex is recruited to the A-site and thereby increasing peptidyl-tRNA slippage; or (ii) a hypomodified peptidyl-tRNA may be more prone to slip than its fully modified counterpart. We propose that the improvement of reading frame maintenance has been and is the major selective factor for the emergence of new modified nucleosides.
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MESH Headings
- Base Sequence
- Codon/genetics
- Escherichia coli/genetics
- Frameshift Mutation
- Genotype
- Models, Genetic
- Oligodeoxyribonucleotides/chemistry
- Phenotype
- RNA, Bacterial/genetics
- RNA, Transfer/chemistry
- RNA, Transfer/genetics
- RNA, Transfer, Amino Acid-Specific/genetics
- RNA, Transfer, Amino Acyl/chemistry
- RNA, Transfer, Amino Acyl/genetics
- RNA, Transfer, Leu/genetics
- RNA, Transfer, Phe/genetics
- RNA, Transfer, Pro/genetics
- RNA, Transfer, Val/genetics
- Reading Frames
- Reference Values
- Salmonella typhimurium/genetics
- beta-Galactosidase/genetics
- beta-Lactamases/genetics
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Affiliation(s)
| | | | | | | | - Glenn R. Björk
- Department of Microbiology, Umeå University, S-90 187 Umeå, Sweden
Corresponding author e-mail:
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8
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Agrawal RK, Spahn CM, Penczek P, Grassucci RA, Nierhaus KH, Frank J. Visualization of tRNA movements on the Escherichia coli 70S ribosome during the elongation cycle. J Cell Biol 2000; 150:447-60. [PMID: 10931859 PMCID: PMC2175196 DOI: 10.1083/jcb.150.3.447] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2000] [Accepted: 06/16/2000] [Indexed: 11/22/2022] Open
Abstract
Three-dimensional cryomaps have been reconstructed for tRNA-ribosome complexes in pre- and posttranslocational states at 17-A resolution. The positions of tRNAs in the A and P sites in the pretranslocational complexes and in the P and E sites in the posttranslocational complexes have been determined. Of these, the P-site tRNA position is the same as seen earlier in the initiation-like fMet-tRNA(f)(Met)-ribosome complex, where it was visualized with high accuracy. Now, the positions of the A- and E-site tRNAs are determined with similar accuracy. The positions of the CCA end of the tRNAs at the A site are different before and after peptide bond formation. The relative positions of anticodons of P- and E-site tRNAs in the posttranslocational state are such that a codon-anticodon interaction at the E site appears feasible.
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Affiliation(s)
- Rajendra K. Agrawal
- Wadsworth Center, Department of Biomedical Sciences, State University of New York, Albany, New York 12201
| | - Christian M.T. Spahn
- Howard Hughes Medical Institute, Health Research, Incorporated at Wadsworth Center, Albany, New York 12201
- Max-Planck-Institut für Molekulare Genetik, Ihnestrasse 73, D-14195 Berlin, Germany
| | - Pawel Penczek
- Wadsworth Center, Department of Biomedical Sciences, State University of New York, Albany, New York 12201
| | - Robert A. Grassucci
- Howard Hughes Medical Institute, Health Research, Incorporated at Wadsworth Center, Albany, New York 12201
| | - Knud H. Nierhaus
- Max-Planck-Institut für Molekulare Genetik, Ihnestrasse 73, D-14195 Berlin, Germany
| | - Joachim Frank
- Wadsworth Center, Department of Biomedical Sciences, State University of New York, Albany, New York 12201
- Howard Hughes Medical Institute, Health Research, Incorporated at Wadsworth Center, Albany, New York 12201
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9
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Abstract
The central process for the transfer of the genetic information from the nucleic acid world into the structure of proteins is the ribosomal elongation cycle, where the sequence of codons is translated into the sequence of amino acids. The nascent polypeptide chain is elongated by one amino acid during the reactions of one cycle. Essentially, three models for the elongation cycle have been proposed. The allosteric three-site model and the hybrid-site model describe different aspects of tRNA binding and do not necessarily contradict each other. However, the alpha-epsilon model is not compatible with both models. The three models are evaluated in the light of recent results on the tRNA localization within the ribosome: the tRNAs of the elongating ribosome could be localized by two different techniques, viz. an advanced method of small-angle neutron scattering and cryo-electron microscopy. The best fit with the biochemical and structural data is obtained with the alpha-epsilon model.
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Affiliation(s)
- C M Spahn
- Max-Planck-Institut für Molekulare Genetik, AG Ribosomen, Berlin, Germany
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10
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Abstract
Mimics recapitulating the structural features of tRNAs are involved in biological processes other than ribosome-dependent protein synthesis. A knowledge of the rules underlying the architecture and function of tRNAs allows the design of non-natural mimics. The study of these mimics sheds light upon links between replication, translation and metabolic pathways, leads to biotechnological applications, and provides experimental and conceptual tools for the exploration of primordial evolutionary processes.
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Affiliation(s)
- R Giegé
- UPR 9002, Structure des Macromolécules Biologiques et Mécanismes de Reconnaissance, Institut de Biologie Moléculaire et Cellulaire du Centre National de la Recherche Scientifique, Strasbourg, France.
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11
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Burkhardt N, Jünemann R, Spahn CM, Nierhaus KH. Ribosomal tRNA binding sites: three-site models of translation. Crit Rev Biochem Mol Biol 1998; 33:95-149. [PMID: 9598294 DOI: 10.1080/10409239891204189] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The first models of translation described protein synthesis in terms of two operationally defined tRNA binding sites, the P-site for the donor substrate, the peptidyl-tRNA, and the A-site for the acceptor substrates, the aminoacyl-tRNAs. The discovery and analysis of the third tRNA binding site, the E-site specific for deacylated tRNAs, resulted in the allosteric three-site model, the two major features of which are (1) the reciprocal relationship of A-site and E-site occupation, and (2) simultaneous codon-anticodon interactions of both tRNAs present at the elongating ribosome. However, structural studies do not support the three operationally defined sites in a simple fashion as three topographically fixed entities, thus leading to new concepts of tRNA binding and movement: (1) the hybrid-site model describes the tRNAs' movement through the ribosome in terms of changing binding sites on the 30S and 50S subunits in an alternating fashion. The tRNAs thereby pass through hybrid binding states. (2) The alpha-epsilon model introduces the concept of a movable tRNA-binding domain comprising two binding sites, termed alpha and epsilon. The translocation movement is seen as a result of a conformational change of the ribosome rather than as a diffusion process between fixed binding sites. The alpha-epsilon model reconciles most of the experimental data currently available.
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MESH Headings
- Allosteric Site/genetics
- Animals
- Base Sequence
- Escherichia coli
- Humans
- Models, Biological
- Models, Molecular
- Molecular Sequence Data
- Peptide Chain Elongation, Translational/genetics
- Protein Biosynthesis
- RNA, Transfer, Amino Acid-Specific/chemistry
- RNA, Transfer, Amino Acid-Specific/genetics
- RNA, Transfer, Amino Acid-Specific/metabolism
- RNA, Transfer, Amino Acyl/chemistry
- RNA, Transfer, Amino Acyl/genetics
- RNA, Transfer, Amino Acyl/metabolism
- Ribosomes/chemistry
- Ribosomes/genetics
- Ribosomes/metabolism
- Structure-Activity Relationship
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Affiliation(s)
- N Burkhardt
- Max-Planck-Institut für Molekulare Genetik, Berlin, Germany
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12
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Nierhaus KH, Wadzack J, Burkhardt N, Jünemann R, Meerwinck W, Willumeit R, Stuhrmann HB. Structure of the elongating ribosome: arrangement of the two tRNAs before and after translocation. Proc Natl Acad Sci U S A 1998; 95:945-50. [PMID: 9448265 PMCID: PMC18634 DOI: 10.1073/pnas.95.3.945] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The ribosome uses tRNAs to translate the genetic information into the amino acid sequence of proteins. The mass ratio of a tRNA to the ribosome is in the order of 1:100; because of this unfavorable value it was not possible until now to determine the location of tRNAs within the ribosome by neutron-scattering techniques. However, the new technique of proton-spin contrast-variation improves the signal-to-noise ratio by more than one order of magnitude, thus enabling the direct determination of protonated tRNAs within a deuterated ribosome for the first time. Here we analyze a pair of ribosomal complexes being either in the pre- or post-translocational states that represent the main states of the elongating ribosome. Both complexes were derived from one preparation. The orientation of both tRNAs within the ribosome and their mutual arrangement are determined by using an electron microscopy model for the Escherichia coli ribosome and the tRNA structure. The mass center of gravity of the (tRNA)2mRNA complex moves within the ribosome by 12 +/- 4 A in the course of translocation as previously reported. The main results of the present analysis are that the mutual arrangement of the two tRNAs does not change on translocation and that the angle between them is, depending on the model used, 110 degrees +/- 10 degrees before and after translocation. The translocational movement of the constant tRNA complex within the ribosome can be described as a displacement toward the head of the 30S subunit combined with a rotational movement by about 18 degrees.
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Affiliation(s)
- K H Nierhaus
- MPI für Molekulare Genetik, AG Ribosomen, Ihnestrasse 73, D-14195 Berlin, Germany.
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13
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Nierhaus KH, Stuhrmann HB, Svergun D. The ribosomal elongation cycle and the movement of tRNAs across the ribosome. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1998; 59:177-204. [PMID: 9427843 DOI: 10.1016/s0079-6603(08)61032-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ribosome research has reached an exciting state, where two lines of experimental research have considerably improved our understanding of the ribosomal functions. On one hand, functional analysis has elucidated principles of both the decoding process and the tRNA movement on the ribosome during translocation. Experimental data leading to current competing models of the ribosomal elongation cycle can be reconciled by a new model, the alpha-epsilon model, according to which both tRNAs are tightly bound to a movable ribosomal domain. This alpha-epsilon domain carries the tRNA2.mRNA complex from the A and P sites to the P and E sites in the course of translocation maintaining the binding of both tRNAs. On the other hand, the location of tRNAs within the elongating ribosome can be directly determined for the first time by neutron scattering and electron microscopy. Both lines of evidence complement each other and define a frame for the first experimentally sound functional model of the elongating ribosome.
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Affiliation(s)
- K H Nierhaus
- Max-Planck-Institut für Molekulare Genetik, Berlin, Germany
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14
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Mueller F, Stark H, van Heel M, Rinke-Appel J, Brimacombe R. A new model for the three-dimensional folding of Escherichia coli 16 S ribosomal RNA. III. The topography of the functional centre. J Mol Biol 1997; 271:566-87. [PMID: 9281426 DOI: 10.1006/jmbi.1997.1212] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We describe the locations of sites within the 3D model for the 16 S rRNA (described in two accompanying papers) that are implicated in ribosomal function. The relevant experimental data originate from many laboratories and include sites of foot-printing, cross-linking or mutagenesis for various functional ligands. A number of the sites were themselves used as constraints in building the 16 S model. (1) The foot-print sites for A site tRNA are all clustered around the anticodon stem-loop of the tRNA; there is no "allosteric" site. (2) The foot-print sites for P site tRNA that are essential for P site binding are similarly clustered around the P site anticodon stem-loop. The foot-print sites in 16 S rRNA helices 23 and 24 are, however, remote from the P site tRNA. (3) Cross-link sites from specific nucleotides within the anticodon loops of A or P site-bound tRNA are mostly in agreement with the model, whereas those from nucleotides in the elbow region of the tRNA (which also exhibit extensive cross-linking to the 50 S subunit) are more widely spread. Again, cross-links to helix 23 are remote from the tRNAs. (4) The corresponding cross-links from E site tRNA are predominantly in helix 23, and these agree with the model. Electron microscopy data are presented, suggestive of substantial conformational changes in this region of the ribosome. (5) Foot-prints for IF-3 in helices 23 and 24 are at a position with close contact to the 50 S subunit. (6) Foot-prints from IF-1 form a cluster around the anticodon stem-loop of A site tRNA, as do also the sites on 16 S rRNA that have been implicated in termination. (7) Foot-print sites and mutations relating to streptomycin form a compact group on one side of the A site anticodon loop, with the corresponding sites for spectinomycin on the other side. (8) Site-specific cross-links from mRNA (which were instrumental in constructing the 16 S model) fit well both in the upstream and downstream regions of the mRNA, and indicate that the incoming mRNA passes through the well-defined "hole" at the head-body junction of the 30 S subunit.
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Affiliation(s)
- F Mueller
- AG-Ribosomen, Max-Planck-Institut für Molekulare Genetik, Ihnestrasse 73, Berlin, 14195, Germany
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15
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Abstract
Others have recently shown that the UUU phenylalanine codon is highly frameshift-prone in the 3'(rightward) direction at pyrimidine 3'contexts. Here, several approaches are used to analyze frameshifting at such sites. The four permutations of the UUU/C (phenylalanine) and CGG/U (arginine) codon pairs were examined because they vary greatly in their expected frameshifting tendencies. Furthermore, these synonymous sites allow direct tests of the idea that codon usage can control frameshifting. Frameshifting was measured for these dicodons embedded within each of two broader contexts: the Escherichia coli prfB (RF2 gene) programmed frameshift site and a 'normal' message site. The principal difference between these contexts is that the programmed frameshift contains a purine-rich sequence upstream of the slippery site that can base pair with the 3'end of 16 S rRNA (the anti-Shine-Dalgarno) to enhance frameshifting. In both contexts frameshift frequencies are highest if the slippery tRNAPhe is capable of stable base pairing in the shifted reading frame. This requirement is less stringent in the RF2 context, as if the Shine-Dalgarno interaction can help stabilize a quasi-stable rephased tRNA:message complex. It was previously shown that frameshifting in RF2 occurs more frequently if the codon 3'to the slippery site is read by a rare tRNA. Consistent with that earlier work, in the RF2 context frameshifting occurs substantially more frequently if the arginine codon is CGG, which is read by a rare tRNA. In contrast, in the 'normal' context frameshifting is only slightly greater at CGG than at CGU. It is suggested that the Shine-Dalgarno-like interaction elevates frameshifting specifically during the pause prior to translation of the second codon, which makes frameshifting exquisitely sensitive to the rate of translation of that codon. In both contexts frameshifting increases in a mutant strain that fails to modify tRNA base A37, which is 3'of the anticodon. Thus, those base modifications may limit frameshifting at UUU codons. Finally, statistical analyses show that UUU Ynn dicodons are extremely rare in E.coli genes that have highly biased codon usage.
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Affiliation(s)
- R Schwartz
- Department of Biology, Wake Forest University, PO Box 7325, Winston-Salem, NC 27109, USA
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16
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Abstract
Major new results in the 3D cryoimaging of ribosomes have advanced our understanding of ribosomal structure and function. For the first time, 3D difference maps have been used to image tRNA molecules in situ. With this new technology, the stage is set for detailed ligand-binding experiments that explore the binding states of elongation factors and tRNA, and that pinpoint locations of proteins and RNA on the surface of the ribosome.
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Affiliation(s)
- J Frank
- Wadsworth Center, New York State Department of Health, State University of New York at Albany, PO Box 509, Empire State Plaza, Albany, NY 12201-0509, USA.
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