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The Ribosomal Stalk Plays a Key Role in IF2-Mediated Association of the Ribosomal Subunits
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
2010 (English)In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 399, no 1, 145-153 p.Article in journal (Refereed) Published
Abstract [en]

Ribosomal "stalk" protein L12 is known to activate translational GTPases EF-G and EF-Tu, but not much is known about its role in relation to other two translational G factors, IF2 and RF3. Here, we have clarified the role of L12 in IF2-mediated initiation of bacterial protein synthesis. With fast kinetics measurements, we have compared L12-depleted 50S subunits with the native ones in subunit association, GTP hydrolysis, Pi (inorganic phosphate) release and IF2 release assays. L12 depletion from 50S subunit slows the subunit association step significantly (similar to 40 fold) only when IF2.GTP is present on the 30S preinitiation complex. This demonstrates that rapid subunit association depends on a specific interaction between the L12 stalk on the 50S subunit and IF2.GTP on the 30S subunit. L12 depletion, however, did not affect the individual rates of the subsequent steps including GTP hydrolysis on IF2 and Pi release. Thus, L12 is not a GTPase activating protein (GAP) for IF2 unlike as suggested for EF-G and EF-Tu.

Place, publisher, year, edition, pages
2010. Vol. 399, no 1, 145-153 p.
Keyword [en]
ribosome, translation initiation, L12, IF2, subunit association
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-136263DOI: 10.1016/j.jmb.2010.04.009ISI: 000278779900012OAI: oai:DiVA.org:uu-136263DiVA: diva2:376574
Available from: 2010-12-11 Created: 2010-12-11 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Ribosomal Stalk Protein L12: Structure, Function and Application
Open this publication in new window or tab >>Ribosomal Stalk Protein L12: Structure, Function and Application
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ribosomal stalk proteins are known to play important role in protein synthesis. The ‘stalk’, an extended structure on the large subunit of the ribosome is composed mainly of two to three dimers of L12 and one L10 protein, which forms the base of the stalk. In E. coli, four copies of L12 molecules exist as dimer of dimers forming the pentameric L8 complex together with L10. This thesis is a collection of four interlinked studies on the structure, function and application of the ribosomal stalk protein L12. In the first study, we have mapped the interaction sites of the four major translation GTPase factors (IF2, EF-Tu, EF-G & RF3) on L12 molecule using heteronuclear NMR spectroscopy. Surprisingly, all these factors produced an overlapping interaction map spanning two α-helices on the C terminal domain of L12, thereby suggesting a general nature of the interaction between L12 and the GTPase factors. L12 is known to stimulate GTPase activity of the elongation factors EF-Tu and EF-G. Here, we have clarified the role of L12 in IF2 mediated initiation of protein synthesis. Our data suggest that rapid subunit association requires a specific interaction between the L12 protein on the 50S and IF2·GTP on the 30S preinitiation complex. We have also shown that L12 is not a GAP for IF2 and GTP hydrolysis triggers IF2 release from the 70S initiation complex. The next question we have addressed is why multiple copies of L12 dimer are needed on the ribosome. For this purpose, we created a pure E. coli strain JE105, where the terminal part of rplJ gene coding for the binding site of one L12 dimer on protein L10 was deleted in the chromosomal locus. Using ribosomes with single L12 dimer we have observed that the rate of the initiation and elongation involving IF2 and EF-G gets most compromised, which in turn decreases the growth rate of the bacteria.  This study also indicates that L12 can interact with different GTPase factors in a specialized manner. Lastly, we have developed an application making advantage of the multiple L12 dimers on the ribosome. By inserting a (His)6-tag at the C-terminus of the L12 protein we have created a novel E. coli strain (JE28), where all ribosomes are tetra-(His)6-tagged. Further, we have developed a single step method for purification of the active (His)6-tagged ribosomes from JE28.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 49 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 848
Keyword
Ribosome, protein synthesis, L12 dimer, initiation, elongation, G factors, and His-tag
National Category
Biochemistry and Molecular Biology
Research subject
Biology with specialization in Molecular Biology
Identifiers
urn:nbn:se:uu:diva-157198 (URN)978-91-554-8144-5 (ISBN)
Public defence
2011-10-06, B41, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2011-09-15 Created: 2011-08-19 Last updated: 2011-11-03Bibliographically approved

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