Journal
NATURE STRUCTURAL & MOLECULAR BIOLOGY
Volume 15, Issue 9, Pages 910-915Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nsmb.1469
Keywords
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Funding
- Volkswagen Stiftung
- Deutsche Forschungsgemeinschaft (DFG) [SF8740, SP 1130/2-1]
- European Union 3D-EM Network of Excellence
- European Union and Senatsverwaltung fur Wissenschaft, Forschung und Kultur Berlin
- Alexander von Humboldt Stiftung
- Medical Research Council [G0600084]
- MRC [G0600084] Funding Source: UKRI
- Medical Research Council [G0600084] Funding Source: researchfish
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EF4 (LepA) is an almost universally conserved translational GTPase in eubacteria. It seems to be essential under environmental stress conditions and has previously been shown to back-translocate the tRNAs on the ribosome, thereby reverting the canonical translocation reaction. In the current work, EF4 was directly visualized in the process of back-translocating tRNAs by single-particle cryo-EM. Using flexible fitting methods, we built a model of ribosome-bound EF4 based on the cryo-EM map and a recently published unbound EF4 X-ray structure. The cryo-EM map establishes EF4 as a noncanonical elongation factor that interacts not only with the elongating ribosome, but also with the back-translocated tRNA in the A-site region, which is present in a previously unseen, intermediate state and deviates markedly from the position of a canonical A-tRNA. Our results, therefore, provide insight into the underlying structural principles governing back-translocation.
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