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

Nat Struct Mol Biol. 2016 Feb;23(2):125-31. doi: 10.1038/nsmb.3160. Epub 2016 Jan 25.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Escherichia coli / chemistry
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Models, Molecular
  • Peptide Initiation Factors / chemistry
  • Peptide Initiation Factors / metabolism*
  • Protein Structure, Tertiary
  • RNA Transport
  • RNA, Transfer, Amino Acyl / chemistry
  • RNA, Transfer, Amino Acyl / metabolism*
  • Ribosome Subunits, Large, Bacterial / chemistry
  • Ribosome Subunits, Large, Bacterial / metabolism*


  • Escherichia coli Proteins
  • LepA protein, E coli
  • Peptide Initiation Factors
  • RNA, Transfer, Amino Acyl
  • tRNA, peptidyl-