Relaxation kinetics of E coli ribosomes: evidence for the reaction of 30S · IF3 complex with 50s ribosomal subunits

• Published in: Biophysical chemistry 1979-05, Vol.9 (4), p.405-412
• Main Authors: Chaires, J.B., Kegeles, G., Wahba, A.J.
• Format: Article
• Language: English
• Subjects: Escherichia coli - metabolism; Kinetics; Light; Magnesium - pharmacology; Peptide Chain Initiation, Translational; Peptide Initiation Factors - metabolism; Pressure; Ribosomes - drug effects; Ribosomes - metabolism; Scattering, Radiation
• ISSN: 0301-4622; 1873-4200
• DOI: 10.1016/0301-4622(75)80056-1

Addition of initiation factor IF3 to solutions of E.coli ribosomes dramatically alters their behavior in pressure-jump relaxation kinetic experiments in which 90° light-scattering is used to monitor the macromolecular reaction. The effect of IF3 on relaxation processes attributed to “tight” couples is strongly dependent on the Mg2+ concentration. At 2.5 mM Mg2+, addition of 1 molar equivalent of IF3 decreases the relaxation amplitude by a factor of 3 relative to ribosome solutions without IF3. However, at 5.0 mM Mg2+, addition of 1 molar equivalent of IF3 produces a marked increase in the relaxation amplitude, by a factor of 2–8 fold relative to ribosomes in the absence of IF3. IF3 has no effect on the relaxation process attributed to “loose” couples at 10 mM Mg2+. While we are unable to propose a precise mechanism for IF3 action with the data on hand, our results require that the 30S · IF3 complex either reacts with the 50S subunit, forming a 70S · IF3 intermediate, or acts as a pool of reactive 30S subunit. Further kinetic evidence is required to distinguish between these possible pathways.