title: Interaction of Escherichia coli translation-initiation factor IF-1 with ribosomes.
abstract: The interaction between Escherichia coli translation-initiation factor IF-1 and ribosomes was studied in binding experiments by Airfuge centrifugation. IF-1 binds to the 30S, but not to the 50S, ribosomal subunit and its binding is strongly stimulated by IF-3 and IF-2, either alone or in combination. From the dependence of the Kd of the 30S-subunit--IF-1 complex on ionic strength, it can be concluded that IF-1 binds primarily via an ionic interaction, most likely with the 16S rRNA, with the minimum number of ion pairs involved being 2.7-3.6. The 30S-subunit--IF-1 interaction is unaffected by temperature changes between 11 degrees C and 44 degrees C and is thus accompanied by a negligible enthalpy change. It is concluded that the interaction is an entropy-driven process triggered mainly by the release of counter ions from the RNA phosphates. Titration of 30S-subunit--IF-1 complexes with 50S subunits causes the ejection of the factor indicating that IF-1 is released from the ribosomes during the subunit association step which marks the transition from a 30S-initiation-complex to a 70S initiation complex.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, West Berlin.
authors.forename: B
authors.initials: B
authors.lastname: Celano
authors.forename: R T
authors.initials: RT
authors.lastname: Pawlik
authors.forename: C O
authors.initials: CO
authors.lastname: Gualerzi
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000235:genetics*; D015977:Eukaryotic Initiation Factor-1; D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D013696:Temperature
chemical_list: D015977:Eukaryotic Initiation Factor-1; D015852:Eukaryotic Initiation Factor-2; D010448:Peptide Initiation Factors; D011506:Proteins; D012269:Ribosomal Proteins