Location of translational initiation factor IF3 on the small ribosomal subunit

John P. Mccutcheon, Rajendra K. Agrawal, Shibu M. Philips, Robert A. Grassucci, Sue Ellen Gerchman, William M. Clemons, V. Ramakrishnan, Joachim Frank

Research output: Contribution to journalArticlepeer-review

116 Scopus citations


The location of translational initiation factor IF3 bound to the 30S subunit of the Thermus thermophilus ribosome has been determined by cryoelectron microscopy. Both the 30S-IF3 complex and control 30S subunit structures were determined to 27-Å resolution. The difference map calculated from the two reconstructions reveals three prominent lobes of positive density. The previously solved crystal structure of IF3 fits very well into two of these lobes, whereas the third lobe probably arises from conformational changes induced in the 30S subunit as a result of IF3 binding. Our placement of IF3 on the 30S subunit allows an understanding in structural terms of the biochemical functions of this initiation factor, namely its ability to dissociate 70S ribosomes into 30S and 50S subunits and the preferential selection of initiator tRNA by IF3 during initiation.

Original languageEnglish (US)
Pages (from-to)4301-4306
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number8
StatePublished - Apr 13 1999
Externally publishedYes


  • Cryoelectron microscopy
  • Ribosome

ASJC Scopus subject areas

  • General


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