EF4 disengages the peptidyl-tRNA CCA end

and facilitates back-translocation on the 70S ribosome.

Nature Structural & Molecular Biology (2016)， Received 16 September 2015, Accepted 11 December 2015, Published online 25 January 2016 ，doi:10.1038/nsmb.3160

EF4 disengages the peptidyl-tRNA CCA end and facilitates back-translocation on the 70S ribosome

Dejiu Zhang, Kaige Yan, Guangqiao Liu, Guangtao Song, Jiejian Luo, Yi Shi, Erchao Cheng, Shan Wu, Taijiao Jiang, Jizhong Lou, Ning Gao & Yan Qin

Abstract:EF4 catalyzes tRNA back-translocation through an unknown mechanism. We report cryo-EM structures of Escherichia coli EF4 in post- and pretranslocational ribosomes (Post– and Pre–EF4) at 3.7- and 3.2-Å resolution, respectively. In Post–EF4, peptidyl-tRNA occupies the peptidyl (P) site, but the interaction between its CCA end and the P loop is disrupted. In Pre–EF4, the peptidyl-tRNA assumes a unique position near the aminoacyl (A) site, denoted the A site/EF4 bound (A/4) site, with a large displacement at its acceptor arm. Mutagenesis analyses suggest that a specific region in the EF4 C-terminal domain (CTD) interferes with base-pairing between the peptidyl-tRNA 3′-CCA and the P loop, whereas the EF4 CTD enhances peptidyl-tRNA interaction at the A/4 site. Therefore, EF4 induces back-translocation by disengaging the tRNA's CCA end from the peptidyl transferase center of the translating ribosome.

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