70S-scanning initiation is a novel and frequent initiation mode of ribosomal translation in bacteria

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...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2016-03, Vol.113 (9), p.E1180-E1189
Main Authors: Yamamoto, Hiroshi, Wittek, Daniela, Gupta, Romi, Qin, Bo, Ueda, Takuya, Krause, Roland, Yamamoto, Kaori, Albrecht, Renate, Pech, Markus, Nierhaus, Knud H.
Format: Article
Language:English
Subjects:
Bacteria
Binding sites
Biological Sciences
Mathematical models
Models, Molecular
Peptide Initiation Factors - metabolism
PNAS Plus
Protein Biosynthesis
Proteins
Ribonucleic acid
Ribosomes - metabolism
RNA
RNA, Messenger - metabolism
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Summary: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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1524554113