title: 70S-scanning initiation is a novel and frequent initiation mode of ribosomal translation in bacteria.
abstract: According to the standard model of bacterial translation initiation, the small ribosomal 30S subunit binds to the initiation site of an mRNA with the help of three initiation factors (IF1-IF3). Here, we describe a novel type of initiation termed "70S-scanning initiation," where the 70S ribosome does not necessarily dissociate after translation of a cistron, but rather scans to the initiation site of the downstream cistron. We detailed the mechanism of 70S-scanning initiation by designing unique monocistronic and polycistronic mRNAs harboring translation reporters, and by reconstituting systems to characterize each distinct mode of initiation. Results show that 70S scanning is triggered by fMet-tRNA and does not require energy; the Shine-Dalgarno sequence is an essential recognition element of the initiation site. IF1 and IF3 requirements for the various initiation modes were assessed by the formation of productive initiation complexes leading to synthesis of active proteins. IF3 is essential and IF1 is highly stimulating for the 70S-scanning mode. The task of IF1 appears to be the prevention of untimely interference by ternary aminoacyl (aa)-tRNA•elongation factor thermo unstable (EF-Tu)•GTP complexes. Evidence indicates that at least 50% of bacterial initiation events use the 70S-scanning mode, underscoring the relative importance of this translation initiation mechanism.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany;
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamamoto
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany;
authors.forename: Daniela
authors.initials: D
authors.lastname: Wittek
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany;
authors.forename: Romi
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany;
authors.forename: Bo
authors.initials: B
authors.lastname: Qin
authors.affiliation: Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba Prefecture 277-8562, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Ueda
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany;
authors.forename: Roland
authors.initials: R
authors.lastname: Krause
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany;
authors.forename: Kaori
authors.initials: K
authors.lastname: Yamamoto
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany;
authors.forename: Renate
authors.initials: R
authors.lastname: Albrecht
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; pech@genzentrum.lmu.de nierhaus@molgen.mpg.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Pech
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Abteilung Vingron, 14195 Berlin, Germany; Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany; pech@genzentrum.lmu.de nierhaus@molgen.mpg.de.
authors.forename: Knud H
authors.initials: KH
authors.lastname: Nierhaus
mesh_terms: D008958:Models, Molecular; D010448:Peptide Initiation Factors / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D010448:Peptide Initiation Factors; D012333:RNA, Messenger
keywords: 30S-binding initiation; 70S-scanning initiation; protein synthesis; ribosomal functions; translational initiation