The ribosome‐bound initiation factor 2 recruits initiator tRNA to the 30S initiation complex |
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| Authors: | Pohl Milon Marcello Carotti Andrey L Konevega Wolfgang Wintermeyer Marina V Rodnina Claudio O Gualerzi |
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| Institution: | 1. Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, G?ttingen, 37077 Germany;2. Laboratory of Genetics, Department of Biology MCA, University of Camerino, Gentille III da Varano, Camerino, 62032 Italy;3. Department of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute, Gatchina, 188300 Russia |
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| Abstract: | Bacterial translation initiation factor 2 (IF2) is a GTPase that promotes the binding of the initiator fMet‐tRNAfMet to the 30S ribosomal subunit. It is often assumed that IF2 delivers fMet‐tRNAfMet to the ribosome in a ternary complex, IF2·GTP·fMet‐tRNAfMet. By using rapid kinetic techniques, we show here that binding of IF2·GTP to the 30S ribosomal subunit precedes and is independent of fMet‐tRNAfMet binding. The ternary complex formed in solution by IF2·GTP and fMet‐tRNA is unstable and dissociates before IF2·GTP and, subsequently, fMet‐tRNAfMet bind to the 30S subunit. Ribosome‐bound IF2 might accelerate the recruitment of fMet‐tRNAfMet to the 30S initiation complex by providing anchoring interactions or inducing a favourable ribosome conformation. The mechanism of action of IF2 seems to be different from that of tRNA carriers such as EF‐Tu, SelB and eukaryotic initiation factor 2 (eIF2), instead resembling that of eIF5B, the eukaryotic subunit association factor. |
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| Keywords: | GTPase FRET rapid filtration stopped‐flow fluorescence |
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