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In the process of protein synthesis, the small (40S) subunit of the eukaryotic ribosome is recruited to the capped 5' end of the mRNA, from which point it scans along the 5' untranslated region in search of a start codon. However, the 40S subunit alone is not capable of functional association with cellular mRNA species; it has to be prepared for the recruitment and scanning steps by interactions with a group of eukaryotic initiation factors (eIFs). In budding yeast, an important subset of these factors (1, 2, 3, and 5) can form a multifactor complex (MFC). Here, we describe cryo-EM reconstructions of the 40S subunit, of the MFC, and of 40S complexes with MFC factors plus eIF1A. These studies reveal the positioning of the core MFC on the 40S subunit, and show how eIF-binding induces mobility in the head and platform and reconfigures the head-platform-body relationship. This is expected to increase the accessibility of the mRNA channel, thus enabling the 40S subunit to convert to a recruitment-competent state.

Original publication

DOI

10.1073/pnas.0606880104

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

03/04/2007

Volume

104

Pages

5788 - 5793

Keywords

5' Untranslated Regions, Codon, Initiator, Cryoelectron Microscopy, Eukaryotic Initiation Factor-1, Eukaryotic Initiation Factor-2, Eukaryotic Initiation Factor-3, Eukaryotic Initiation Factor-5, Models, Chemical, Models, Molecular, Protein Binding, Protein Biosynthesis, Protein Structure, Secondary, Protein Subunits, RNA, Fungal, RNA, Messenger, Ribosomes, Saccharomyces cerevisiae