The effects of initiation factors IF‐1 and IF‐3 on the dissociation of <i>escherichia coli</i> 70 S ribosomes

Dottavio-Martin, Diane; Suttle, D P; Ravel, Joanne M.

doi:10.1016/0014-5793(79)80062-9

Cited by 17 publications

(16 citation statements)

References 21 publications

(4 reference statements)

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“…It enhances the dissociation and association rate for 70S ribosomes (46,59), primarily through the stimulating effect on the activity of IF2 and IF3 (174). Interaction between IF2 and the 30S ribosomal subunit is favored when IF1 is bound, and the release of IF2 is indirectly promoted when IF1 is ejected (27,136,222).…”

Section: Translation Initiation Factorsmentioning

confidence: 99%

Initiation of Protein Synthesis in Bacteria

Laursen

Sørensen

Mortensen

et al. 2005

Microbiol Mol Biol Rev

530

506

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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

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Section: Translation Initiation Factorsmentioning

confidence: 99%

Initiation of Protein Synthesis in Bacteria

Laursen

Sørensen

Mortensen

et al. 2005

Microbiol Mol Biol Rev

530

506

View full text Add to dashboard Cite

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“…Binding of IF3 chl to 30 S Subunits-The indicated concentrations of IF3 chl and chloroplast 30 S subunits were incubated in a total volume of 250 l in 50 mM Tris-HCl, pH 7.8, 10 mM dithiothreitol (DTT), 50 mM NH 4 Cl, and 10 mM MgCl 2 at room temperature for 5 min. The mixture was applied to a 5-ml 10 -30% linear sucrose gradient prepared in the same buffer except that the concentration of Tris-HCl was reduced to 10 mM.…”

Section: Materials-[mentioning

confidence: 99%

“…33 for E. coli IF3. A complex carrying AcPhe-tRNA bound to chloroplast 30 S subunits (AcPhe-tRNA⅐poly(U)⅐30 S) was formed by incubation of chloroplast 30 S subunits (10 pmol) with poly(U) (2.5 g) and AcPhe-tRNA (4 pmol) in a reaction mixture (50 l) containing 50 mM Tris-HCl, pH 7.8, 10 mM dithiothreitol, 50 mM NH 4 Cl, and 15 mM MgCl 2 . After incubation at 37°C for 30 min, the mixture was diluted 2-fold with 50 mM Tris-HCl, pH 7.8, and 50 mM NH 4 Cl in the presence of different concentrations of IF3 chl or its derivatives.…”

Section: Materials-[mentioning

confidence: 99%

“…Mixtures were incubated for an additional 5 min at 37°C. The destabilization of the complex by IF3 chl was monitored following dilution with 1 ml of prewarmed dilution buffer (50 mM Tris-HCl, pH 7.8, 10 mM dithiothreitol, 50 mM NH 4 Cl, and 7.5 mM MgCl 2 ). These reaction mixtures were incubated at 37°C for 5 min.…”

Section: Materials-[mentioning

confidence: 99%

“…During initiation, IF3 binds to the 30 S subunit and shifts the equilibrium between the ribosome and its subunits toward dissociation (3,4). IF1 and IF2 bind to the 30 S⅐IF3 complex.…”

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confidence: 99%

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Regulation of the Activity of Chloroplast Translational Initiation Factor 3 by NH2- and COOH-Terminal Extensions

Yu¹,

Spremulli²

1998

Journal of Biological Chemistry

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The mature form of the chloroplast translational initiation factor 3 (IF3 chl ) from Euglena gracilis consists of an internal region homologous to prokaryotic IF3 flanked by long NH 2 -and COOH-terminal extensions. Sequences in these extensions reduce the activity of the homology domain in promoting initiation complex formation with chloroplast mRNAs and 30 S ribosomal subunits. A series of deletions of the NH 2 -and COOH-terminal extensions of IF3 chl were constructed and tested for their effects on the activity of the homology domain. About half of the inhibitory effect arises from sequences within 9 residues of the junction between the NH 2 -terminal extension and the homology domain. The remaining inhibitory effect is the result of sequences in the COOH-terminal extension. The equilibrium constant governing the binding of the homology domain of IF3 chl to 30 S subunits is estimated to be 1.3 ؋ 10 7 M ؊1 . Sequences close to the junction of the NH 2 -terminal extension and the homology domain reduce this binding constant about 10-fold. Sequences in the COOH-terminal extension have a similar negative effect. The negative effects of these two regions are cumulative, resulting in a 100-fold reduction of the binding constant. The 9 residues at the NH 2 -terminal extension effectively prevent the proofreading activity of IF3 chl . The entire COOHterminal extension reduces the proofreading ability by about half. These results are discussed in terms of the proposed three-dimensional structure of the homology domain of IF3 chl .Three translational initiation factors (IF1, IF2, and IF3) 1 are required for the initiation of protein synthesis in Escherichia coli (1, 2). During initiation, IF3 binds to the 30 S subunit and shifts the equilibrium between the ribosome and its subunits toward dissociation (3, 4). IF1 and IF2 bind to the 30 S⅐IF3 complex. The initiation factor⅐30 S complex binds the mRNA and fMet-tRNA, resulting in the formation of an unstable preinitiation complex. This complex is converted into a stable initiation complex when the initiator tRNA has been selected and codon-antidocon interaction occurs (5, 6). IF3 has three major functions: 1) it binds to the 30 S subunit, preventing the joining of 50 S subunits (1-3, 5); 2) it increases the affinity of IF1 and IF2 for the 30 S subunit and stimulates fMet-tRNA binding to the 30 S subunit by promoting the conversion of the preinitiation complex to the initiation complex (7, 8); and 3) it proofreads the selection of fMet-tRNA at an AUG initiation codon (9 -14).The chloroplast translational initiation factors are postulated to be functionally analogous to their E. coli counterparts. Only IF2 chl and IF3 chl from Euglena gracilis have been purified (15, 16). Both of these factors are nuclear-encoded proteins in this organism (17, 18). IF3 chl has been resolved into three forms, ␣, ␤, and ␥. The ␣ form has a molecular mass of about 34 kDa, whereas the ␤ and ␥ forms have molecular masses of about 45 kDa (16). In contrast, E. coli IF3 has a molecular mass of 20 kD...

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Mechanism of protein biosynthesis in prokaryotic cells

Pon¹,

Gualerzi²

1984

FEBS Letters

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To define the step at which translational initiation factor IF1 excercises its stimulation, initial rate kinetic analyses of 30 S initiation complex formation were carried out in the presence and absence of this factor. It was shown that, without affecting the affinity of the ribosomes either for the initiator tRNA or for the poly(AUG) used as template, IF1 increases approximately 2.5-fold the limiting V,,of the 'pre-ternary complex' + ternary complex transition which represents the rate-limiting step in 30 S initiation complex formation. This kinetic effect titrates with the 30s ribosomal subunit which must therefore represent the target of IF1 action. Translational initiation Initiation factor 30 S initiation complex Kinetics Ribosome

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The effects of initiation factors IF‐1 and IF‐3 on the dissociation of escherichia coli 70 S ribosomes

Cited by 17 publications

References 21 publications

Initiation of Protein Synthesis in Bacteria

Initiation of Protein Synthesis in Bacteria

Regulation of the Activity of Chloroplast Translational Initiation Factor 3 by NH2- and COOH-Terminal Extensions

Mechanism of protein biosynthesis in prokaryotic cells

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