1
|
The molecular choreography of protein synthesis: translational control, regulation, and pathways. Q Rev Biophys 2016; 49:e11. [PMID: 27658712 DOI: 10.1017/s0033583516000056] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Translation of proteins by the ribosome regulates gene expression, with recent results underscoring the importance of translational control. Misregulation of translation underlies many diseases, including cancer and many genetic diseases. Decades of biochemical and structural studies have delineated many of the mechanistic details in prokaryotic translation, and sketched the outlines of eukaryotic translation. However, translation may not proceed linearly through a single mechanistic pathway, but likely involves multiple pathways and branchpoints. The stochastic nature of biological processes would allow different pathways to occur during translation that are biased by the interaction of the ribosome with other translation factors, with many of the steps kinetically controlled. These multiple pathways and branchpoints are potential regulatory nexus, allowing gene expression to be tuned at the translational level. As research focus shifts toward eukaryotic translation, certain themes will be echoed from studies on prokaryotic translation. This review provides a general overview of the dynamic data related to prokaryotic and eukaryotic translation, in particular recent findings with single-molecule methods, complemented by biochemical, kinetic, and structural findings. We will underscore the importance of viewing the process through the viewpoints of regulation, translational control, and heterogeneous pathways.
Collapse
|
2
|
Chen J, Petrov A, Tsai A, O'Leary SE, Puglisi JD. Coordinated conformational and compositional dynamics drive ribosome translocation. Nat Struct Mol Biol 2013; 20:718-27. [PMID: 23624862 PMCID: PMC3883222 DOI: 10.1038/nsmb.2567] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 03/07/2013] [Indexed: 12/15/2022]
Abstract
During translation elongation, the compositional factors, elongation factor G (EF-G; encoded by fusA) and transfer RNA (tRNA), alternately bind to the ribosome to direct protein synthesis, in turn regulating the conformation of the ribosome. Here, we use single-molecule fluorescence with zero-mode waveguides to correlate directly ribosome conformations and compositions during multiple rounds of elongation at high factor concentrations in Escherichia coli. Our results show that EF-G-GTP continuously samples both rotational sates of the ribosome, binding with higher affinity to the rotated state. Upon successful accommodation into the rotated ribosome, the EF-G-ribosome complex evolves through several rate-limiting conformational changes and the hydrolysis of GTP, which results in a transition back to the non-rotated state, in turn driving translocation and facilitating both EF-G-GDP and E-site tRNA release. These experiments highlight the power of tracking single-molecule conformation and composition simultaneously in real-time.
Collapse
Affiliation(s)
- Jin Chen
- Department of Applied Physics, Stanford University, Stanford, California, USA
| | | | | | | | | |
Collapse
|
3
|
Yu H, Chan YL, Wool IG. The identification of the determinants of the cyclic, sequential binding of elongation factors tu and g to the ribosome. J Mol Biol 2009; 386:802-13. [PMID: 19154738 DOI: 10.1016/j.jmb.2008.12.071] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Revised: 11/21/2008] [Accepted: 12/29/2008] [Indexed: 11/16/2022]
Abstract
Experiments dedicated to gaining an understanding of the mechanism underlying the orderly, sequential association of elongation factor Tu (EF-Tu) and elongation factor G (EF-G) with the ribosome during protein synthesis were undertaken. The binding of one EF is always followed by the binding of the other, despite the two sharing the same-or a largely overlapping-site and despite the two having isosteric structures. Aminoacyl-tRNA, peptidyl-tRNA, and deacylated-tRNA were bound in various combinations to the A-site, P-site, or E-site of ribosomes, and their effect on conformation in the peptidyl transferase center, the GTPase-associated center, and the sarcin/ricin domain (SRD) was determined. In addition, the effect of the ribosome complexes on sensitivity to the ribotoxins sarcin and pokeweed antiviral protein and on the binding of EF-G*GTP were assessed. The results support the following conclusions: the EF-Tu ternary complex binds to the A-site whenever it is vacant and the P-site has peptidyl-tRNA; and association of the EF-Tu ternary complex is prevented, simply by steric hindrance, when the A-site is occupied by peptidyl-tRNA. On the other hand, the affinity of the ribosome for EF-G*GTP is increased when peptidyl-tRNA is in the A-site, and the increase is the result of a conformational change in the SRD. We propose that peptidyl-tRNA in the A-site is an effector that initiates a series of changes in tertiary interactions between nucleotides in the peptidyl transferase center, the SRD, and the GTPase-associated center of 23S rRNA; and that the signal, transmitted through a transduction pathway, informs the ribosome of the position of peptidyl-tRNA and leads to a conformational change in the SRD that favors binding of EF-G.
Collapse
Affiliation(s)
- Huijun Yu
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
| | | | | |
Collapse
|
4
|
Hansson S, Singh R, Gudkov AT, Liljas A, Logan DT. Crystal structure of a mutant elongation factor G trapped with a GTP analogue. FEBS Lett 2005; 579:4492-7. [PMID: 16083884 DOI: 10.1016/j.febslet.2005.07.016] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2005] [Revised: 06/21/2005] [Accepted: 07/06/2005] [Indexed: 11/23/2022]
Abstract
Elongation factor G (EF-G) is a G protein factor that catalyzes the translocation step in protein synthesis on the ribosome. Its GTP conformation in the absence of the ribosome is currently unknown. We present the structure of a mutant EF-G (T84A) in complex with the non-hydrolysable GTP analogue GDPNP. The crystal structure provides a first insight into conformational changes induced in EF-G by GTP. Comparison of this structure with that of EF-G in complex with GDP suggests that the GTP and GDP conformations in solution are very similar and that the major contribution to the active GTPase conformation, which is quite different, therefore comes from its interaction with the ribosome.
Collapse
Affiliation(s)
- Sebastian Hansson
- Department of Molecular Biophysics, Lund University, Box 124, S-211 00 Lund, Sweden
| | | | | | | | | |
Collapse
|
5
|
Hansson S, Singh R, Gudkov AT, Liljas A, Logan DT. Structural insights into fusidic acid resistance and sensitivity in EF-G. J Mol Biol 2005; 348:939-49. [PMID: 15843024 DOI: 10.1016/j.jmb.2005.02.066] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Revised: 02/25/2005] [Accepted: 02/27/2005] [Indexed: 11/26/2022]
Abstract
Fusidic acid (FA) is a steroid antibiotic commonly used against Gram positive bacterial infections. It inhibits protein synthesis by stalling elongation factor G (EF-G) on the ribosome after translocation. A significant number of the mutations conferring strong FA resistance have been mapped at the interfaces between domains G, III and V of EF-G. However, direct information on how such mutations affect the structure has hitherto not been available. Here we present the crystal structures of two mutants of Thermus thermophilus EF-G, G16V and T84A, which exhibit FA hypersensitivity and resistance in vitro, respectively. These mutants also have higher and lower affinity for GTP respectively than wild-type EF-G. The mutations cause significant conformational changes in the switch II loop that have opposite effects on the position of a key residue, Phe90, which undergoes large conformational changes. This correlates with the importance of Phe90 in FA sensitivity reported in previous studies. These structures substantiate the importance of the domain G/domain III/domain V interfaces as a key component of the FA binding site. The mutations also cause subtle changes in the environment of the "P-loop lysine", Lys25. This led us to examine the conformation of the equivalent residue in all structures of translational GTPases, which revealed that EF-G and eEF2 form a group separate from the others and suggested that the role of Lys25 may be different in the two groups.
Collapse
Affiliation(s)
- Sebastian Hansson
- Department of Molecular Biophysics, Lund University, Box 124, S-221 00 Lund, Sweden
| | | | | | | | | |
Collapse
|
6
|
Laursen BS, Sørensen HP, Mortensen KK, Sperling-Petersen HU. Initiation of protein synthesis in bacteria. Microbiol Mol Biol Rev 2005; 69:101-23. [PMID: 15755955 PMCID: PMC1082788 DOI: 10.1128/mmbr.69.1.101-123.2005] [Citation(s) in RCA: 415] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Valuable information on translation initiation is available from biochemical data and recently solved structures. We present a detailed description of current knowledge about the structure, function, and interactions of the individual components involved in bacterial translation initiation. The first section describes the ribosomal features relevant to the initiation process. Subsequent sections describe the structure, function, and interactions of the mRNA, the initiator tRNA, and the initiation factors IF1, IF2, and IF3. Finally, we provide an overview of mechanisms of regulation of the translation initiation event. Translation occurs on ribonucleoprotein complexes called ribosomes. The ribosome is composed of a large subunit and a small subunit that hold the activities of peptidyltransfer and decode the triplet code of the mRNA, respectively. Translation initiation is promoted by IF1, IF2, and IF3, which mediate base pairing of the initiator tRNA anticodon to the mRNA initiation codon located in the ribosomal P-site. The mechanism of translation initiation differs for canonical and leaderless mRNAs, since the latter is dependent on the relative level of the initiation factors. Regulation of translation occurs primarily in the initiation phase. Secondary structures at the mRNA ribosomal binding site (RBS) inhibit translation initiation. The accessibility of the RBS is regulated by temperature and binding of small metabolites, proteins, or antisense RNAs. The future challenge is to obtain atomic-resolution structures of complete initiation complexes in order to understand the mechanism of translation initiation in molecular detail.
Collapse
Affiliation(s)
- Brian Søgaard Laursen
- Department of Molecular Biology, Aarhus University, Gustav Wieds vej 10C, DK-8000 Aarhus C, Denmark
| | | | | | | |
Collapse
|
7
|
Sharma D, Southworth DR, Green R. EF-G-independent reactivity of a pre-translocation-state ribosome complex with the aminoacyl tRNA substrate puromycin supports an intermediate (hybrid) state of tRNA binding. RNA (NEW YORK, N.Y.) 2004; 10:102-13. [PMID: 14681589 PMCID: PMC1370522 DOI: 10.1261/rna.5148704] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Following peptide-bond formation, the mRNA:tRNA complex must be translocated within the ribosomal cavity before the next aminoacyl tRNA can be accommodated in the A site. Previous studies suggested that following peptide-bond formation and prior to EF-G recognition, the tRNAs occupy an intermediate (hybrid) state of binding where the acceptor ends of the tRNAs are shifted to their next sites of occupancy (the E and P sites) on the large ribosomal subunit, but where their anticodon ends (and associated mRNA) remain fixed in their prepeptidyl transferase binding states (the P and A sites) on the small subunit. Here we show that pre-translocation-state ribosomes carrying a dipeptidyl-tRNA substrate efficiently react with the minimal A-site substrate puromycin and that following this reaction, the pre-translocation-state bound deacylated tRNA:mRNA complex remains untranslocated. These data establish that pre-translocation-state ribosomes must sample or reside in an intermediate state of tRNA binding independent of the action of EF-G.
Collapse
Affiliation(s)
- Divya Sharma
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | | | | |
Collapse
|
8
|
Cameron DM, Thompson J, March PE, Dahlberg AE. Initiation factor IF2, thiostrepton and micrococcin prevent the binding of elongation factor G to the Escherichia coli ribosome. J Mol Biol 2002; 319:27-35. [PMID: 12051934 DOI: 10.1016/s0022-2836(02)00235-8] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The bacterial translational GTPases (initiation factor IF2, elongation factors EF-G and EF-Tu and release factor RF3) are involved in all stages of translation, and evidence indicates that they bind to overlapping sites on the ribosome, whereupon GTP hydrolysis is triggered. We provide evidence for a common ribosomal binding site for EF-G and IF2. IF2 prevents the binding of EF-G to the ribosome, as shown by Western blot analysis and fusidic acid-stabilized EF-G.GDP.ribosome complex formation. Additionally, IF2 inhibits EF-G-dependent GTP hydrolysis on 70 S ribosomes. The antibiotics thiostrepton and micrococcin, which bind to part of the EF-G binding site and interfere with the function of the factor, also affect the function of IF2. While thiostrepton is a strong inhibitor of EF-G-dependent GTP hydrolysis, GTP hydrolysis by IF2 is stimulated by the drug. Micrococcin stimulates GTP hydrolysis by both factors. We show directly that these drugs act by destabilizing the interaction of EF-G with the ribosome, and provide evidence that they have similar effects on IF2.
Collapse
Affiliation(s)
- Dale M Cameron
- School of Microbiology and Immunology, University of New South Wales, Sydney, NSW 2052, Australia
| | | | | | | |
Collapse
|
9
|
Yang X, Ishiguro EE. Involvement of the N terminus of ribosomal protein L11 in regulation of the RelA protein of Escherichia coli. J Bacteriol 2001; 183:6532-7. [PMID: 11673421 PMCID: PMC95482 DOI: 10.1128/jb.183.22.6532-6537.2001] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Amino acid-deprived rplK (previously known as relC) mutants of Escherichia coli cannot activate (p)ppGpp synthetase I (RelA) and consequently exhibit relaxed phenotypes. The rplK gene encodes ribosomal protein L11, suggesting that L11 is involved in regulating the activity of RelA. To investigate the role of L11 in the stringent response, a derivative of rplK encoding L11 lacking the N-terminal 36 amino acids (designated 'L11) was constructed. Bacteria overexpressing 'L11 exhibited a relaxed phenotype, and this was associated with an inhibition of RelA-dependent (p)ppGpp synthesis during amino acid deprivation. In contrast, bacteria overexpressing normal L11 exhibited a typical stringent response. The overexpressed 'L11 was incorporated into ribosomes and had no effect on the ribosome-binding activity of RelA. By several methods (yeast two-hybrid, affinity blotting, and copurification), no direct interaction was observed between the C-terminal ribosome-binding domain of RelA and L11. To determine whether the proline-rich helix of L11 was involved in RelA regulation, the Pro-22 residue was replaced with Leu by site-directed mutagenesis. The overexpression of the Leu-22 mutant derivative of L11 resulted in a relaxed phenotype. These results indicate that the proline-rich helix in the N terminus of L11 is involved in regulating the activity of RelA.
Collapse
Affiliation(s)
- X Yang
- Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada
| | | |
Collapse
|
10
|
La Teana A, Gualerzi CO, Dahlberg AE. Initiation factor IF 2 binds to the alpha-sarcin loop and helix 89 of Escherichia coli 23S ribosomal RNA. RNA (NEW YORK, N.Y.) 2001; 7:1173-9. [PMID: 11497435 PMCID: PMC1370164 DOI: 10.1017/s1355838201010366] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
During initiation of protein synthesis in bacteria, translation initiation factor IF2 is responsible for the recognition of the initiator tRNA (fMet-tRNA). To perform this function, IF2 binds to the ribosome interacting with both 30S and 50S ribosomal subunits. Here we report the topographical localization of translation initiation factor IF2 on the 70S ribosome determined by base-specific chemical probing. Our results indicate that IF2 specifically protects from chemical modification two sites in domain V of 23S rRNA, namely A2476 and A2478, and residues around position 2660 in domain VI, the so-called sarcin-ricin loop. These footprints are generated by IF2 regardless of the presence of fMet-tRNA, GTP, mRNA, and IF1. IF2 causes no specific protection of 16S rRNA. We observe a decreased reactivity of residues A1418 and A1483, which is an indication that the initiation factor has a tightening effect on the association of ribosomal subunits. This result, confirmed by sucrose density gradient analysis, seems to be a universally conserved property of IF2.
Collapse
Affiliation(s)
- A La Teana
- Insitute of Biochemistry, University of Ancona, Italy
| | | | | |
Collapse
|
11
|
Koosha H, Cameron D, Andrews K, Dahlberg AE, March PE. Alterations in the peptidyltransferase and decoding domains of ribosomal RNA suppress mutations in the elongation factor G gene. RNA (NEW YORK, N.Y.) 2000; 6:1166-73. [PMID: 10943895 PMCID: PMC1369990 DOI: 10.1017/s1355838200000534] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The translocation stage of protein synthesis is a highly conserved process in all cells. Although the components necessary for translocation have been delineated, the mechanism of this activity has not been well defined. Ribosome movement on template mRNA must allow for displacement of tRNA-mRNA complexes from the ribosomal A to P sites and P to E sites, while ensuring rigid maintenance of the correct reading frame. In Escherichia coli, translocation of the ribosome is promoted by elongation factor G (EF-G). To examine the role of EF-G and rRNA in translocation we have characterized mutations in rRNA genes that can suppress a temperature-sensitive (ts) allele of fusA, the gene in E. coli that encodes EF-G. This analysis was performed using the ts E. coli strain PEM100, which contains a point mutation within fusA. The ts phenotype of PEM100 can be suppressed by either of two mutations in the decoding region of the 16S rRNA when present in combination with a mutation at position 2058 in the peptidyltransferase domain of the 23S rRNA. Communication between these ribosomal domains is essential for coordinating the events of the elongation cycle. We propose a model in which EF-G promotes translocation by modulating this communication, thereby increasing the efficiency of this fundamental process.
Collapse
MESH Headings
- Blotting, Western
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Hydroxylamine/pharmacology
- Mutation
- Mutation, Missense
- Peptide Elongation Factor G/genetics
- Peptidyl Transferases/genetics
- Phenotype
- Plasmids/genetics
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/genetics
- RNA, Ribosomal, 23S/chemistry
- RNA, Ribosomal, 23S/genetics
- Temperature
- Translocation, Genetic
Collapse
Affiliation(s)
- H Koosha
- School of Microbiology and Immunology, The University of New South Wales, Sydney, Australia
| | | | | | | | | |
Collapse
|
12
|
Affiliation(s)
- K S Wilson
- Center for Molecular Biology of RNA, Sinsheimer Laboratories, University of California, Santa Cruz 95064, USA
| | | |
Collapse
|
13
|
Wilson KS, Noller HF. Mapping the position of translational elongation factor EF-G in the ribosome by directed hydroxyl radical probing. Cell 1998; 92:131-9. [PMID: 9489706 DOI: 10.1016/s0092-8674(00)80905-8] [Citation(s) in RCA: 192] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The interaction of translational elongation factor EF-G with the ribosome in the posttranslocational state has been mapped by directed hydroxyl radical probing. Localized hydroxyl radicals were generated from Fe(II) tethered to 18 different sites on the surface of EF-G bound to the ribosome. Cleavages in ribosomal RNA were mapped, providing proximity relationships between specific sites of EF-G and rRNA elements of the ribosome. Collectively, these data provide a set of constraints by which EF-G can be positioned unambiguously in the ribosome at low resolution. The proximities of different domains of EF-G to well-characterized elements of rRNA have additional implications for the mechanism of protein synthesis.
Collapse
Affiliation(s)
- K S Wilson
- Center for Molecular Biology of RNA, Sinsheimer Laboratories, University of California, Santa Cruz 95064, USA
| | | |
Collapse
|
14
|
Czworkowski J, Moore PB. The elongation phase of protein synthesis. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1996; 54:293-332. [PMID: 8768078 DOI: 10.1016/s0079-6603(08)60366-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- J Czworkowski
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA
| | | |
Collapse
|
15
|
Moazed D, Robertson JM, Noller HF. Interaction of elongation factors EF-G and EF-Tu with a conserved loop in 23S RNA. Nature 1988; 334:362-4. [PMID: 2455872 DOI: 10.1038/334362a0] [Citation(s) in RCA: 414] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The elongation factors EF-Tu and EF-G interact with ribosomes during protein synthesis: EF-Tu presents incoming aminoacyl transfer RNA to the programmed ribosome as an EF-Tu-GTP-tRNA ternary complex and EF-G promotes translocation of peptidyl-tRNA and its associated messenger RNA from the A to the P site after peptidyl transfer. Both events are accompanied by ribosome-dependent GTP hydrolysis. Here we use chemical probes to investigate the possible interaction of these factors with ribosomal RNA in E. coli ribosomes. We observe EF-G-dependent footprints in vitro and in vivo around position 1,067 in domain II of 23S rRNA, and in the loop around position 2,660 in domain VI.EF-Tu gives an overlapping footprint in vitro at positions 2,655 and 2,661, but shows no effect at position 1,067. The 1,067 region is the site of interaction of the antibiotic thiostrepton, which prevents formation of the EF-G-GTP-ribosome complex and is a site for interaction with the GTPase-related protein L11 (ref. 3). The universally conserved loop in the 2,660 region is the site of attack by the RNA-directed cytotoxins alpha-sarcin and ricin, whose effects abolish translation and include the loss of elongation factor-dependent functions in eukaryotic ribosomes.
Collapse
Affiliation(s)
- D Moazed
- Thimann Laboratories, University of California, Santa Cruz 95064
| | | | | |
Collapse
|
16
|
Van Noort JM, Kraal B, Bosch L. GTPase center of elongation factor Tu is activated by occupation of the second tRNA binding site. Proc Natl Acad Sci U S A 1986; 83:4617-21. [PMID: 3014498 PMCID: PMC323792 DOI: 10.1073/pnas.83.13.4617] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Interaction of the elongation factor EF-Tu with the antibiotic kirromycin results in activation of the GTPase center of the factor and in induction of an additional tRNA binding site (tRNA binding site II to distinguish it from the classical tRNA binding site I). Activation of the GTPase center under these conditions is stimulated by addition of tRNA. Two-fold evidence is presented that this stimulation is due to tRNA binding to site II rather than to site I. First, a strong correlation is observed between stimulation of the GTPase activity and enhancement of the reactivity of Cys-81 of EF-Tu toward N-ethylmaleimide at various concentrations of aminoacyl-tRNA, deacylated tRNA, and N-acetylaminoacyl-tRNA. The latter effects signal tRNA binding to site II. Stimulation of the kirromycin-induced GTPase activity by tRNA binding to the factor also occurs when binding to site I is completely abolished. Such an abolishment was achieved by treating EF-Tu extensively with the thiol reagent L-1-tosylamido-2-phenylethyl chloromethyl ketone. EF-Tu X GTP thus treated has lost its ability to protect the ester bond of aminoacyl-tRNA. The relevance of these data for the sequence of events during protein synthesis and for control of translational fidelity is discussed.
Collapse
|
17
|
Uchiumi T, Kikuchi M, Terao K, Iwasaki K, Ogata K. Cross-linking of elongation factor 2 to rat-liver ribosomal proteins by 2-iminothiolane. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 156:37-48. [PMID: 3956508 DOI: 10.1111/j.1432-1033.1986.tb09545.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Complexes containing rat liver 80S ribosomes treated with puromycin and high concentrations of KCl, elongation factor 2 (EF-2) from pig liver, and guanosine 5'-[beta, gamma-methylene]triphosphate were prepared. Neighboring proteins in the complexes were cross-linked with the bifunctional reagent 2-iminothiolane. Proteins were extracted and then separated into 22 fractions by chromatography on carboxymethylcellulose of which seven fractions were used for further analyses. Each protein fraction was subjected to diagonal polyacrylamide/sodium dodecyl sulfate gel electrophoresis. Nine cross-linked protein pairs between EF-2 and ribosomal proteins were shifted from the line formed with monomeric proteins. The spots of ribosomal proteins cross-linked to EF-2 were cut out from the gel plate and labelled with 125I. The labelled protein was extracted from the gel and identified by three kinds of two-dimensional gel electrophoresis, followed by autoradiography. The following proteins of both large and small subunits were identified: L9, L12, L23, LA33 (acidic protein of Mr 33000), P2, S6 and S23/S24, and L3 and L4 in lower yields. The results are discussed in relation to the topographies of ribosomal proteins in large and small subunits. Furthermore we found new neighboring protein pairs in large subunits, LA33-L11 and LA33-L12.
Collapse
|
18
|
|
19
|
Tate WP, Hornig H, Lührmann R. Recognition of termination codon by release factor in the presence of a tRNA-occupied A site. Evidence for flexibility in accommodation of the release factor on the ribosome. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(17)44465-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
20
|
Abstract
When bottromycin A2 was added to an in vitro protein synthesis system carried out by naturally occurring polysomes, it inhibited protein synthesis effectively. Examination of the 3 steps of peptide chain elongation revealed that the binding of aminoacyl-tRNA to the polyribosomes was inhibited by bottromycin A2. In contrast, we concluded that the peptide bond formation and the translocation steps in this system were not inhibited by bottromycin A2 on the basis of the following observations: (1) The break-down of polysomes, which is dependent on EFG, puromycin and RR (ribosome releasing) factor, was insensitive to bottromycin A2; (2) The puromycin dependent release of polypeptide from polysomes, with or without EFG, was not inhibited by bottromycin A2. Thus bottromycin specifically interferes with proper functioning of the A sites of polysomes. This is consistent with the results obtained using the model system with synthetic polynucleotides.
Collapse
|
21
|
Ohsawa H, Ohsawa E, Giovane A, Gualerzi C. Chemical modification in situ of Escherichia coli 50 S ribosomal proteins by the site-specific reagent pyridoxal phosphate. Inactivation of the elongation factor-G-dependent GTPase and of the association with the small ribosomal subunit. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)33234-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
22
|
Sköld SE. Chemical cross-linking of elongation factor G to both subunits of the 70-S ribosomes from Escherichia coli. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 127:225-9. [PMID: 6754377 DOI: 10.1111/j.1432-1033.1982.tb06859.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Ribosomal proteins situated at or near the binding site of elongation factor G (EF-G) on the Escherichia coli ribosome have been identified by use of the bifunctional, cleavable cross-linker, dimethyl-4,9-diaza-5,8-dioxo-6,7-dihydroxy-dodecanebisimidate. Five different bimolecular EF-G x ribosomal-protein complexes were isolated electrophoretically. The ribosomal proteins found in each of these complexes were identified as the 50-S-subunit proteins L6, L7/L12 and L14 and the 30-S-subunit proteins S12 and S19. In the presence of thiostrepton, which prevents binding of EF-G to the ribosome, there was a considerable decrease in the yield of each of these cross-linked complexes. The data suggest that EF-G is bound close to the ribosomal subunit interface.
Collapse
|
23
|
Nierhaus KH, Wittmann HG. Ribosomal function and its inhibition by antibiotics in prokaryotes. THE SCIENCE OF NATURE - NATURWISSENSCHAFTEN 1980; 67:234-50. [PMID: 6901544 DOI: 10.1007/bf01054532] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Most of the known antibiotics act at the level of protein biosynthesis probably due to the extraordinary complexity of the translation machinery which can be interfered with at many points. At first a survey is given of our present knowledge covering the structure and function of the prokaryotic ribosome. The most important antibiotics acting at the translational level are integrated into this network of data. The binding sites and the inhibition mechanisms of the drugs, together with the ribosomal components altered in resistant mutants are described. Finally, the points of interference with the translational machinery are indicated in an extended scheme of ribosomal functions.
Collapse
|
24
|
Abstract
The relationship between the binding domains of elongation factor G(EF-G) and stringent factor (SF) on ribosomes was studied. The binding of highly purified, radioactively labeled, protein factors to ribosomes was monitored with a column system. The data show that binding of EF-G to ribosomes in the presence of fusidic acid and GDP or of the noncleavable analogue GDPCP prevents subsequent binding of SF to ribosomes. In addition, stabilization of the EF-G-ribosome complex by fusidic acid inhibits SF's enzymatic activities. Removal of protein L7/L12 from ribosomes leads to weaker binding of EF-G, while SF's binding and activity are unaffected. In the absence of L7/L12, EF-G-dependent inhibition of SF binding and function is reduced. The data presented in this report suggest that these two factors bind at overlapping, or at least interacting, ribosomal domains.
Collapse
|
25
|
Miller DL. THE BINDING OF AAtRNA TO PROKARYOTIC RIBOSOMES. Gene Expr 1978. [DOI: 10.1016/b978-0-08-022624-8.50012-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
|
26
|
Bermek E. Mechanisms in polypeptide chain elongation on ribosomes. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1978; 21:63-100. [PMID: 358280 DOI: 10.1016/s0079-6603(08)60267-6] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
|
27
|
Richter D, Isono K. The mechanism of protein synthesis-initiation, elongation and termination in translation of genetic messeges. Curr Top Microbiol Immunol 1977; 76:83-125. [PMID: 334484 DOI: 10.1007/978-3-642-66653-7_3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
|
28
|
Cross-linking of initiation factor IF2 to proteins L7/L12 in 70 S ribosomes of Escherichia coli. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(19)57002-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
|
29
|
Spirin AS, Asatryan LS. The effect of ribosomal peptidyl-transferase inhibitors is antagonized by elongation factor G with GTP. FEBS Lett 1976; 70:101-4. [PMID: 791676 DOI: 10.1016/0014-5793(76)80735-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
30
|
Lin L, Bodley JW. Binding interactions between radiolabeled Escherichia coli elongation factor G and the ribosome. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)33719-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
|
31
|
San Millan MJ, Vazquez D, Modolell J. The interaction of fusidic acid with peptidyl-transfer-ribonucleic-acid - ribosome complexes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1975; 57:431-40. [PMID: 1100406 DOI: 10.1111/j.1432-1033.1975.tb02318.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The inhibitory action of fusidic acid on peptide-chain elongation was studied with systems in vitro directed by either polyuridylic acid or endogenous messenger (Escherichia coli polysomes washed with 1 M NH4Cl) or R17 RNA, and supplemented with either crude or purified elongation factors. In all cases strong inhibition of synthesis required high concentrations of the antibiotic (approx. 1 mM), while a similar inhibition of the EF-G-plus-ribosome-dependent GTP hydrolysis required between 10 and 100 times less antibiotic. Since most of the GTP hydrolysis observed was presumably due to free ribosomes (without aminoacyl-tRNA or peptidyl-tRNA), fusidic acid seemed to interact far more easily with these ribosomes than with ribosomes engaged in peptide-chain elongation. The role of the GDP-EF-G-ribosome-fusidic acid complex in the inhibition of polypeptide synthesis was assessed by measuring formation of this complex on polysomes engaged in peptide-chain elongation. Using purified elongation factors the complex formed on only 25-35% of ribosomes, as measured either by retention of [3H]GDP or by hydrolysis of [3H, gamma-32P]GTP. In contrast, with crude factors (S 100 extract) it formed on more than 70% of ribosomes. The results are compatible with the postulated role of the complex in polypeptide synthesis inhibition (blockade of the ribosomal acceptor site and subsequent inhibition of aminoacyl-tRNA binding) and indicate that formation of the complex takes place by overriding the control that prevents interaction of EF-G when the donor site is occupied by peptidyl-tRNA. In the polyuridylic-acid-directed system for synthesis of oligophenylalanine the antibiotic inhibits every round of peptide elongation, including dipeptide formation, to roughly the same extent.
Collapse
|
32
|
Abstract
Sporangiomycin and micrococcin inhibit the binding of aminoacyl-transfer ribonucleic acid into the ribosomal A site in intact bacterial protoplasts. They also prevent the assembly of [ribosome-elongation factor G-guanine nucleotide] complexes in vitro and compete with [35S]thiostrepton for ribosomal binding sites. We conclude that micrococcin and sporangiomycin block the ribosomal A site in the vicinity of the complex guanosine triphosphatase center and so resemble thiostrepton in their modes of action.
Collapse
|
33
|
Pranger MH, Van der Zeijst BA. Inhibiton by fusidic acid of the reaction between puromycin and donor site bound N-acetyl-phenylalanyl-tRNA on yeast ribosomes. FEBS Lett 1975; 51:177-9. [PMID: 1091507 DOI: 10.1016/0014-5793(75)80881-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
34
|
|
35
|
Otaka T, Kaji A. Micrococcin: acceptor-site-specific inhibitor of protein synthesis. EUROPEAN JOURNAL OF BIOCHEMISTRY 1974; 50:101-6. [PMID: 4615898 DOI: 10.1111/j.1432-1033.1974.tb03876.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
|
36
|
Sarkar P, Stringer EA, Maitra U. Thiostrepton inhibition of initiation factor 1 activity in polypeptide chain initiation in Escherichia coli. Proc Natl Acad Sci U S A 1974; 71:4986-90. [PMID: 4612536 PMCID: PMC434024 DOI: 10.1073/pnas.71.12.4986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Thiostrepton, a peptide antibiotic, inhibits the GTP-dependent 70S initiation complex formation (as measured by binding of fMet-tRNA to ribosomes and concomitant hydrolysis of GTP) only when initiation factor 1 is present to permit catalytic recycling of initiation factor 2 in the initiation reaction. When initiation factor 1 is absent, the binding of fMet-tRNA and GTP hydrolysis occur stoichiometrically with respect to initiation factor 2, and thiostrepton has no effect on either reaction under these conditions. Detailed analysis of this inhibition process shows that thiostrepton prevents catalytic recycling of initiation factor 2 by blocking the action of initiation factor 1, which is required for the dissociation of initiation factor 2 from the 70S initiation complex. This dissociation is necessary for the catalytic reutilization of initiation factor 2 in the initiation reaction. The antibiotic does not directly inhibit GTP hydrolysis per se in initiation. The inhibition of fMet-tRNA binding to ribosomes by thiostrepton is also dependent on the concentration of GTP; the inhibition is most pronounced at low concentrations of GTP, but at a high molar ratio of GTP to thiostrepton, the inhibition is completely abolished.
Collapse
|
37
|
Baksht E, de Groot ND. The enzymatic binding of aminoacyl-tRNA to reticulocyte ribosomes: the stimulatory effect of donor site bound peptidyl-tRNA. Mol Biol Rep 1974; 1:493-7. [PMID: 4616173 DOI: 10.1007/bf00360677] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
|
38
|
Lockwood AH, Sarkar P, Maitra U, Brot N, Weissbach H. Effect of Thiostrepton on Polypeptide Chain Initiation in Escherichia coli. J Biol Chem 1974. [DOI: 10.1016/s0021-9258(20)79892-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
39
|
|
40
|
Grummt F, Grummt I, Erdmann VA. ATPase and GTPase activities isolated from rat liver ribosomes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1974; 43:343-8. [PMID: 4365186 DOI: 10.1111/j.1432-1033.1974.tb03418.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
|
41
|
|
42
|
|
43
|
Ganoza MC, Fox JL. Isolation of a Soluble Factor Needed for Protein Synthesis with Various Messenger Ribonucleic Acids Other Than Poly(U). J Biol Chem 1974. [DOI: 10.1016/s0021-9258(19)42938-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
44
|
Hradec J, Dusek Z, Mach O. Influence of cholesteryl 14-methylhexadecanoate on some ribosomal functions required for peptide elongation. Biochem J 1974; 138:147-54. [PMID: 4595729 PMCID: PMC1166189 DOI: 10.1042/bj1380147] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
1. Polyribosomes and ribosomal subunits from rat liver were adsorbed on a cellulosic ion-exchange adsorbent, freeze-dried and extracted with organic solvents. The activity of extracted particles in peptide elongation was tested in the presence of purified peptideelongation factors. 2. Chloroform-methanol mixture (2:1, v/v) extracted 1.87+/-0.15 pmol of cholesteryl 14-methylhexadecanoate/pmol of the smaller ribosomal subunit and 0.92+/-0.11 pmol/pmol of the larger subunit. 3. In the presence of transferase I, extracted polyribosomes and 40S subunits bound more phenylalanyl-tRNA than did control non-extracted particles. The same binding as in control mixtures was obtained with extracted particles supplemented with cholesteryl 14-methylhexadecanoate in quantities corresponding to those extracted. 4. The polymerization of phenylalanine was greatly decreased with extracted polyribosomes and subunits and addition of the cholesteryl ester could not fully restore the original activity. 5. Extraction significantly decreased the activity of the P site of peptidyl transferase and normal activity was recovered after the addition of the ester. The A site of peptidyl transferase in extracted polyribosomes showed an increased activity when compared with non-extracted polyribosomes. 6. Cholesteryl 14-methylhexadecanoate apparently affects the function of the ribosomal A site and peptidyl transferase site and probably also that of the guanosine triphosphatase site and P site. The presence of different amounts of the ester in polyribosomes may be one of the mechanisms modulating peptide elongation at the ribosomal level.
Collapse
|
45
|
The Role of Ribosomal Proteins L7 and L12 in Polypeptide Chain Initiation in Escherichia coli. J Biol Chem 1974. [DOI: 10.1016/s0021-9258(19)42962-1] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
|
46
|
Moore PB, Engelman DM, Schoenborn BP. Asymmetry in the 50S ribosomal subunit of Escherichia coli. Proc Natl Acad Sci U S A 1974; 71:172-6. [PMID: 4589891 PMCID: PMC387959 DOI: 10.1073/pnas.71.1.172] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
A substantial separation of the centers of mass of the protein and RNA portions of the 50S ribosomal subunit has been achieved using neutron scattering. This separation reveals that the subunit has a protein-rich side, a finding which is inconsistent with many models proposed for the structure. By analyzing the variation of the radius of gyration of the subunit under conditions in which the contributions of the protein and RNA were separately enhanced by deuteration and comparing these radii to the undeuterated subunit radius, we have obtained the following values. The radius of gyration of the whole particle is 78.0 +/- 0.95 A, that of the RNA moiety is 72.5 +/- 1.5 A, and that of the protein is 73.4 +/- 2.0 A. These data give a separation of the centers of mass of the RNA and protein distributions of 57.7 +/- 10 A.
Collapse
|
47
|
Lucas-Lenard J, Beres L. 2. Protein Synthesis—Peptide Chain Elongation. ACTA ACUST UNITED AC 1974. [DOI: 10.1016/s1874-6047(08)60134-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
|
48
|
Brot N, Tate WP, Caskey CT, Weissbach H. The requirement for ribosomal proteins L7 and L12 in peptide-chain termination. Proc Natl Acad Sci U S A 1974; 71:89-92. [PMID: 4589896 PMCID: PMC387938 DOI: 10.1073/pnas.71.1.89] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Proteins L7 and L12 from 50S ribosomal subunits of Escherichia coli are required for peptidechain termination. This termination process is inhibited by thiostrepton. Since both thiostrepton-treated ribosomes and those depleted of L7 and L12 have a markedly reduced ability to form release factor.UA[(3)H]A.ribosome complexes, the binding of release factors to the ribosome appears to be the primary site of inhibition.
Collapse
|
49
|
Relation between the Ribosomal Sites Involved in Initiation and Elongation of Polypeptide Chains. J Biol Chem 1974. [DOI: 10.1016/s0021-9258(19)43036-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
50
|
Nombela C, Ochoa S. Conformational control of the interaction of eukaryotic elongation factors EF-1 and EF-2 with ribosomes. Proc Natl Acad Sci U S A 1973; 70:3556-60. [PMID: 4519645 PMCID: PMC427279 DOI: 10.1073/pnas.70.12.3556] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
As in the case with prokaryotic systems, Artemia salina elongation factors EF-1 and EF-2 interact with a common site or with closely overlapping sites on the Artemia ribosome. This feature of ribosomal design must restrict interaction with the ribosome to only one of the factors at alternating steps of chain elongation. In support of this view we find that EF-1, but not EF-2, interacts with the post-translocation ribosome, whereas the reverse is true of the pre-translocation ribosome. Conformational changes probably account for the alternating selectivity of the translating ribosome for each elongation factor.
Collapse
|