Yeast eukaryotic initiation factor 4B remodels the mRNA entry site on the small ribosomal subunit

Abstract

Eukaryotic initiation factor 4B (eIF4B) belongs to the eIF4 group of factors that help in mRNA recruitment to the ribosomal preinitiation complex (PIC) in all eukaryotic organisms. eIF4B stimulates the helicase activity of eIF4A and helps in the formation of the 48S PIC by facilitating mRNA recruitment. However, there is no clear understanding of the location of eIF4B on the 40S and how eIF4B helps in the recruitment of mRNAs. In this work using cryo-electron microscopy, we show that yeast eIF4B binds to the 40S ribosomal subunit at the mRNA entry channel making contacts with ribosomal proteins uS10, uS3, and eS10 and ribosomal rRNA helix h16. The yeast eIF4B position on the 40S overlaps with the RRM domain of eIF3g indicating that the binding of eIF4B may trigger the relocation of the eIF3 b-g-i module to the subunit interface. The 40S head is in partially open conformation that may facilitate the release of eIF3j and hence aid mRNA recruitment and scanning. The structural analysis of yeast eIF4B-bound ribosomal complex provides insight into possible events during mRNA recruitment.