eIF5B and eIF1A reorient initiator tRNA to allow ribosomal subunit joining

Nature. 2022 Jul;607(7917):185-190. doi: 10.1038/s41586-022-04858-z. Epub 2022 Jun 22.


Translation initiation defines the identity and quantity of a synthesized protein. The process is dysregulated in many human diseases1,2. A key commitment step is when the ribosomal subunits join at a translation start site on a messenger RNA to form a functional ribosome. Here, we combined single-molecule spectroscopy and structural methods using an in vitro reconstituted system to examine how the human ribosomal subunits join. Single-molecule fluorescence revealed when the universally conserved eukaryotic initiation factors eIF1A and eIF5B associate with and depart from initiation complexes. Guided by single-molecule dynamics, we visualized initiation complexes that contained both eIF1A and eIF5B using single-particle cryo-electron microscopy. The resulting structure revealed how eukaryote-specific contacts between the two proteins remodel the initiation complex to orient the initiator aminoacyl-tRNA in a conformation compatible with ribosomal subunit joining. Collectively, our findings provide a quantitative and architectural framework for the molecular choreography orchestrated by eIF1A and eIF5B during translation initiation in humans.

MeSH terms

  • Cryoelectron Microscopy
  • Eukaryotic Initiation Factor-1* / metabolism
  • Eukaryotic Initiation Factors* / genetics
  • Humans
  • RNA, Transfer, Met* / genetics
  • RNA, Transfer, Met* / metabolism
  • Ribosome Subunits* / chemistry
  • Ribosome Subunits* / metabolism
  • Single Molecule Imaging


  • Eukaryotic Initiation Factor-1
  • Eukaryotic Initiation Factors
  • RNA, Transfer, Met
  • eukaryotic initiation factor-5B
  • eukaryotic peptide initiation factor-1A