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Research Explains Molecular Mechanism of Ribosomal Process

Jan 26, 2016

New research by Prof. QIN Yan of the Institute of Biophysics (IBP) of the Chinese Academy of Sciences and other scientists has shown the molecular mechanism for ribosome back-movement during protein translation. The study, entitled EF4 Disengages the Peptidyl-tRNA CCA End and Facilitates Back-translocation on the 70S Ribosome, was published online on Jan. 25 in Natural Structural & Molecular Biology, 

Ribosomes are protein translation factories. During translation, a ribosome moves along mRNA in the direction of 5’ to 3’; this motion is catalyzed by the translation elongation factor G (EF-G). However, discovery of the highly conserved translation elongation factor 4 (EF4) by Dr. QIN Yan and the tRNA motions it induces indicates that tRNAs in the P- and E-site of the translating ribosome can move backwards; namely, the ribosome can move backwards along the mRNA in the direction of 3’ to 5’. 

QIN’s group has focused on ribosome translocation research since her lab was set up at IBP in 2006. In 2012 and 2014, QIN’s group twice published the molecular structure and mechanism of EF4- and EF-G-induced translation regulation in the journal Nature Structural & Molecular Biology (Figure A). 

In the current research, Prof. QIN and Dr. GAO Ning of Tsinghua University combined cryo-EM and biochemical tools to characterize E. coli translating ribosomes assembled with EF4, seeking to understand the molecular mechanism by which EF4 performs its unique back-translocase function. 

The researchers found that EF4 triggers tRNA back-movement by a specific region in the EF4 C-terminal domain (CTD) interfering with base-pairing between the peptidyl-tRNA 3′-CCA and the P-loop of the ribosome peptidyl transferase center. Therefore, EF4 induces back-translocation by disengaging the tRNA’s CCA end (the head) from the peptidyl transferase center of the translating ribosome. 

 

Mechanism of tRNA forward or backward movement catalyzed by EF-G and EF4, respectively. a) EF-G and EF4-catalyze ribosomal movement along mRNA; b) EF-G catalyzes tRNA forward movement by pushing the tRNA foot; EF4 catalyzes tRNA backward movement by pulling the tRNA head (Image by QIN Yan)  

Prof. QIN is supported by an IBP “One-Three-Five” Goal-oriented Project and the Key Laboratory of RNA Biology at IBP. This work was supported by grants from the Ministry of Science and Technology of China, the National Natural Science Foundation of China and the Strategic Priority Research Program of the Chinese Academy of Sciences.

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