GTP Hydrolysis by eIF5B in the Last Step of Translation Initiation Is Activated by a Rotation of the Small Ribosomal Subunit.

Abstract

Placement of an initiator aminoacyl-tRNA [(f)Met-tRNA[Formula]] base paired with the AUG initiation codon of a messenger RNA (mRNA) is the first step of translation. The eukaryotic translation factor eIF5B or its bacerial homologue IF2 facilitate the correct positioning of initiator tRNA in the P site of the ribosome. We report the electron cryomicroscopy (cryoEM) structure of a stabilized intermediate state of a yeast 80S/tRNAiMet/eIF5B complex at 3.6 [A] resolution. The structure shows how a universally conserved tyrosine couples the rotational state of the small ribosomal subunit with GTP hydrolysis.