Involvement of protein IF2 N domain in ribosomal subunit joining revealed from architecture and function of the full-length initiation factor

Proc Natl Acad Sci U S A. 2013 Sep 24;110(39):15656-61. doi: 10.1073/pnas.1309578110. Epub 2013 Sep 12.


Translation initiation factor 2 (IF2) promotes 30S initiation complex (IC) formation and 50S subunit joining, which produces the 70S IC. The architecture of full-length IF2, determined by small angle X-ray diffraction and cryo electron microscopy, reveals a more extended conformation of IF2 in solution and on the ribosome than in the crystal. The N-terminal domain is only partially visible in the 30S IC, but in the 70S IC, it stabilizes interactions between IF2 and the L7/L12 stalk of the 50S, and on its deletion, proper N-formyl-methionyl(fMet)-tRNA(fMet) positioning and efficient transpeptidation are affected. Accordingly, fast kinetics and single-molecule fluorescence data indicate that the N terminus promotes 70S IC formation by stabilizing the productive sampling of the 50S subunit during 30S IC joining. Together, our data highlight the dynamics of IF2-dependent ribosomal subunit joining and the role played by the N terminus of IF2 in this process.

Keywords: integrated structural biology; protein synthesis.

Publication types

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

MeSH terms

  • Cryoelectron Microscopy
  • Models, Molecular
  • Mutant Proteins / metabolism
  • Peptide Chain Initiation, Translational
  • Prokaryotic Initiation Factor-2 / chemistry*
  • Prokaryotic Initiation Factor-2 / metabolism*
  • Prokaryotic Initiation Factor-2 / ultrastructure
  • Protein Binding
  • Protein Structure, Tertiary
  • Ribosome Subunits / metabolism*
  • Ribosome Subunits, Large, Bacterial
  • Ribosome Subunits, Small, Bacterial
  • Scattering, Small Angle
  • Structure-Activity Relationship
  • Thermus thermophilus / metabolism*
  • X-Ray Diffraction


  • Mutant Proteins
  • Prokaryotic Initiation Factor-2

Associated data

  • PDB/3J4J