Cryo-EM study of start codon selection during archaeal translation initiation

Nat Commun. 2016 Nov 7;7:13366. doi: 10.1038/ncomms13366.


Eukaryotic and archaeal translation initiation complexes have a common structural core comprising e/aIF1, e/aIF1A, the ternary complex (TC, e/aIF2-GTP-Met-tRNAiMet) and mRNA bound to the small ribosomal subunit. e/aIF2 plays a crucial role in this process but how this factor controls start codon selection remains unclear. Here, we present cryo-EM structures of the full archaeal 30S initiation complex showing two conformational states of the TC. In the first state, the TC is bound to the ribosome in a relaxed conformation with the tRNA oriented out of the P site. In the second state, the tRNA is accommodated within the peptidyl (P) site and the TC becomes constrained. This constraint is compensated by codon/anticodon base pairing, whereas in the absence of a start codon, aIF2 contributes to swing out the tRNA. This spring force concept highlights a mechanism of codon/anticodon probing by the initiator tRNA directly assisted by aIF2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anticodon / metabolism
  • Archaea / physiology*
  • Archaeal Proteins / physiology*
  • Archaeal Proteins / ultrastructure
  • Base Pairing / physiology
  • Codon, Initiator / metabolism
  • Codon, Initiator / ultrastructure
  • Cryoelectron Microscopy
  • Peptide Chain Initiation, Translational / physiology*
  • Peptide Initiation Factors / physiology*
  • Peptide Initiation Factors / ultrastructure
  • RNA, Messenger / metabolism
  • RNA, Transfer, Met / physiology
  • Ribosome Subunits, Small, Archaeal / physiology
  • Ribosome Subunits, Small, Archaeal / ultrastructure*


  • Anticodon
  • Archaeal Proteins
  • Codon, Initiator
  • IF2 protein, archaeal
  • Peptide Initiation Factors
  • RNA, Messenger
  • RNA, Transfer, Met