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Pre-binding of small protein B to a stalled ribosome triggers trans-translation
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology.
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2004 In: J Biol Chem, ISSN 25, Vol. 279, 25978-85 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2004. Vol. 279, 25978-85 p.
URN: urn:nbn:se:uu:diva-92944OAI: oai:DiVA.org:uu-92944DiVA: diva2:166272
Available from: 2005-04-22 Created: 2005-04-22Bibliographically approved
In thesis
1. Finding the unknowns in trans-translation
Open this publication in new window or tab >>Finding the unknowns in trans-translation
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Hitta de okända faktorerna för trans-translation
Abstract [en]

Ribosomes stalled on problematic mRNAs can be rescued by a mechanism called trans-translation. This mechanism employs a dual transfer-messenger RNA molecule (tmRNA) together with a helper protein (SmpB).

In this work we have used an in vitro translation system with pure components to further clarify the roles of tmRNA and SmpB in trans-translation.

We found that SmpB binds ribosomes in vivo and in vitro independently of tmRNA presence and is essential for tmRNA binding and trans-peptidation. We show that two SmpB molecules can bind per ribosome, that SmpB does not leave the ribosome after trans-peptidation and that SmpB pre-bound to the ribosome can trigger trans-translation.

We demonstrated that the rate of trans-transfer of a peptide from the P-site tRNA to Ala-tmRNA and the efficiency by which Ala-tmRNA competes with peptide release factors decrease with increasing the mRNA length downstream from the P site of the ribosome. We showed that trans-translation is strongly stimulated by RelE cleavage of A-site mRNA. We concluded that tmRNA action in vivo must always be preceded by mRNA truncation.

We showed that rapid release of truncated mRNAs from the ribosome requires translocation of the peptidyl-tmRNA into the ribosomal P site, which is strictly EF-G dependent. mRNA release is slowed down by strong Shine and Dalgarno like sequences upstream the A site and by long 3’-extensions downstream from the P-site codon.

Footprinting was used to monitor SmpB binding to tmRNA, ribosomes and subunits and to study tmRNA interactions with the ribosome at distinct trans-translation stages. We confirmed that two SmpB molecules bind per ribosome and interact with nucleotides below the L7/L12-stalk on the 50S subunit and near the subunit interface on the 30S. We showed that tmRNA is mostly in complex with SmpB in vivo and during trans-translation. Specific cleavage patterns of tmRNA were observed at different stages of trans-translation, but the overall tmRNA conformation seems to be maintained during the whole process.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 69 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 44
Molecular biology, trans-translation, tmRNA, SmpB, kinetics, footprinting, Molekylärbiologi
National Category
Biochemistry and Molecular Biology
urn:nbn:se:uu:diva-5756 (URN)91-554-6226-X (ISBN)
Public defence
2005-05-19, B41, BMC, Husargatan 3, Uppsala, 13:15
Available from: 2005-04-22 Created: 2005-04-22Bibliographically approved

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