Structure of the Translation Preinitiation Complex from Wheat Germ Extract

Translation preinitiation complexes are typical components of the cytoplasm of eukaryotic cells, consisting of 40S ribosomal subunits bound to initiation factors. Actively studied in mammals and protozoa, these complexes are involved in the initiation of mRNA translation. We studied the abundance and structure of plant preinitiation complexes using single particle cryo-EM analysis of wheat germ extract preparations. Approximately 29% of free 40S subunits form a complex with the initiation factors eIF3 and eIF1A. The structure of the complex was reconstructed with overall resolution better than 3 Å and the core of factor eIF3 with a resolution of 3.6 Å. These are the first data on the structure of initiation ribosomal complex in plants. We constructed the atomic models of the iIF3 core and distal subunits; these models had notable differences comparing to those in mammalian cells.