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3215591 
Journal Article 
EF4 disengages the peptidyl-tRNA CCA end and facilitates back-translocation on the 70S ribosome 
Zhang, D; Yan, K; Liu, G; Song, G; Luo, J; Shi, Y; Cheng, E; Wu, S; Jiang, T; Lou, J; Gao, N; Qin, Y 
2016 
23 
2 
125-131 
English 
26809121 
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.