eIF3 Peripheral Subunits Rearrangement after mRNA Binding and Start-Codon Recognition

• Published in: Molecular cell 2016-07, Vol.63 (2), p.206-217
• Main Authors: Simonetti, Angelita, Brito Querido, Jailson, Myasnikov, Alexander G., Mancera-Martinez, Eder, Renaud, Adeline, Kuhn, Lauriane, Hashem, Yaser
• Format: Article
• Language: English
• Subjects: Animals; beta-Globins; beta-Globins - chemistry; beta-Globins - metabolism; Binding Sites; Biochemistry, Molecular Biology; Codon, Initiator; cryo-EM; eIF3; eIF3 peripheral subunits; Eukaryotic Initiation Factor-1; Eukaryotic Initiation Factor-1 - chemistry; Eukaryotic Initiation Factor-1 - metabolism; Eukaryotic Initiation Factor-2; Eukaryotic Initiation Factor-2 - chemistry; Eukaryotic Initiation Factor-2 - metabolism; Eukaryotic Initiation Factor-3; Eukaryotic Initiation Factor-3 - chemistry; Eukaryotic Initiation Factor-3 - metabolism; eukaryotic translation initiation; Humans; Life Sciences; Models, Molecular; Molecular biology; Multiprotein Complexes; Nucleic Acid Conformation; Protein Binding; Protein Biosynthesis; Protein Conformation; Protein Subunits; Rabbits; ribosome; Ribosomes; Ribosomes - chemistry; Ribosomes - metabolism; RNA, Messenger; RNA, Messenger - chemistry; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Transfer; RNA, Transfer - chemistry; RNA, Transfer - metabolism; Structure-Activity Relationship
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2016.05.033

mRNA translation initiation in eukaryotes requires the cooperation of a dozen eukaryotic initiation factors (eIFs) forming several complexes, which leads to mRNA attachment to the small ribosomal 40S subunit, mRNA scanning for start codon, and accommodation of initiator tRNA at the 40S P site. eIF3, composed of 13 subunits, 8 core (a, c, e, f, h, l, k, and m) and 5 peripheral (b, d, g, i, and j), plays a central role during this process. Here we report a cryo-electron microscopy structure of a mammalian 48S initiation complex at 5.8 Å resolution. It shows the relocation of subunits eIF3i and eIF3g to the 40S intersubunit face on the GTPase binding site, at a late stage in initiation. On the basis of a previous study, we demonstrate the relocation of eIF3b to the 40S intersubunit face, binding below the eIF2-Met-tRNAiMet ternary complex upon mRNA attachment. Our analysis reveals the deep rearrangement of eIF3 and unravels the molecular mechanism underlying eIF3 function in mRNA scanning and timing of ribosomal subunit joining. [Display omitted] •Several subunits of eIF3 relocate upon mRNA binding and start-codon recognition•mRNA binding leads to the relocation of eIF3b to interact with eIF2 ternary complex•eIF3i+g relocate to the 40S intersubunit face after start-codon recognition•eIF3b and eIF1 reposition the eIF2 ternary complex and assist in scanning Protein synthesis initiation in mammals requires the assembly of a dozen initiation factors, in which eIF3 has a pivotal role. Simonetti et al. report by cryo-EM the large-scale conformational changes of several subunits of eIF3 responsible for the regulation of several key steps, such as mRNA scanning and timing of ribosomal subunit joining.