Large-Scale Movements of IF3 and tRNA during Bacterial Translation Initiation

Cell. 2016 Sep 22;167(1):133-144.e13. doi: 10.1016/j.cell.2016.08.074.


In bacterial translational initiation, three initiation factors (IFs 1-3) enable the selection of initiator tRNA and the start codon in the P site of the 30S ribosomal subunit. Here, we report 11 single-particle cryo-electron microscopy (cryoEM) reconstructions of the complex of bacterial 30S subunit with initiator tRNA, mRNA, and IFs 1-3, representing different steps along the initiation pathway. IF1 provides key anchoring points for IF2 and IF3, thereby enhancing their activities. IF2 positions a domain in an extended conformation appropriate for capturing the formylmethionyl moiety charged on tRNA. IF3 and tRNA undergo large conformational changes to facilitate the accommodation of the formylmethionyl-tRNA (fMet-tRNA(fMet)) into the P site for start codon recognition.

Keywords: IF1; IF2; IF3; cryo-EM; fMet-tRNA; initiation; ribosome; start codon; structures; translation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Codon, Initiator*
  • Cryoelectron Microscopy
  • Crystallography
  • Peptide Chain Initiation, Translational*
  • Prokaryotic Initiation Factor-3 / chemistry*
  • Protein Conformation
  • RNA, Messenger / chemistry*
  • RNA, Transfer, Met / chemistry*
  • Ribosome Subunits, Small, Bacterial / chemistry*
  • Thermus thermophilus / genetics
  • Thermus thermophilus / metabolism*


  • Codon, Initiator
  • Prokaryotic Initiation Factor-3
  • RNA, Messenger
  • RNA, Transfer, Met
  • fMet-tRNA(fMet)
  • tRNA, formylmethionine-