Hepatitis-C-virus-like internal ribosome entry sites displace eIF3 to gain access to the 40S subunit

• Published in: Nature (London) 2013-11, Vol.503 (7477), p.539-543
• Main Authors: Hashem, Yaser, des Georges, Amedee, Dhote, Vidya, Langlois, Robert, Liao, Hstau Y., Grassucci, Robert A., Pestova, Tatyana V., Hellen, Christopher U. T., Frank, Joachim
• Format: Article
• Language: English
• Subjects: 101/28; 13/44; 631/337/574/1789; 631/535/1258/1259; 631/57/2265; 82/80; Animals; Binding, Competitive; Classical Swine Fever Virus - genetics; Cryoelectron Microscopy; Eukaryotic Initiation Factor-3 - chemistry; Eukaryotic Initiation Factor-3 - metabolism; Eukaryotic Initiation Factor-3 - ultrastructure; Genetic aspects; Hepatitis; Hepatitis C virus; Hog cholera; Humanities and Social Sciences; Humans; letter; Messenger RNA; Microscopy; Models, Molecular; multidisciplinary; Mutation; Properties; Protein Biosynthesis; Rabbits; Regulatory Sequences, Ribonucleic Acid - genetics; Ribosome Subunits, Small, Eukaryotic - chemistry; Ribosome Subunits, Small, Eukaryotic - metabolism; Ribosome Subunits, Small, Eukaryotic - ultrastructure; Ribosomes; Ribosomes - chemistry; Ribosomes - metabolism; Ribosomes - ultrastructure; RNA, Viral - genetics; RNA, Viral - metabolism; Science; Transfer RNA
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature12658

A sub-nanometre reconstruction of a 40S complex containing eIF3 and a hepatitis C virus (HCV)-like internal ribosome entry site (IRES) shows that the IRES displaces eIF3 from the 40S and sequesters it to gain access to the 40S subunit. Internal ribosome entry sites promote viral takeover Although most cellular messenger RNAs contain a 5′ cap structure, some viral mRNAs lack this, and instead use an internal ribosome entry site (IRES) to guide assembly of the 48S ribosome initiation complex. One type of hepatitis C virus-like IRES interacts with the initiation factor eIF3; previous work suggested that the location of the IRES and eIF3 would overlap on the 40S subunit, so the importance of this novel interaction was unclear. In this work, Joachim Frank and colleagues have generated a sub-nanometre reconstruction of a 40S complex containing eIF3 and a hepatitis C virus-like IRES. They find that in the complex, eIF3 is transferred from the 40S subunit onto the IRES, thereby sequestering it. The authors suggest that this may help to direct translation towards viral mRNAs, as cellular mRNAs require eIF3 to form a pre-initiation complex. Hepatitis C virus (HCV) and classical swine fever virus (CSFV) messenger RNAs contain related (HCV-like) internal ribosome entry sites (IRESs) that promote 5′-end independent initiation of translation, requiring only a subset of the eukaryotic initiation factors (eIFs) needed for canonical initiation on cellular mRNAs 1 . Initiation on HCV-like IRESs relies on their specific interaction with the 40S subunit 2 , 3 , 4 , 5 , 6 , 7 , 8 , which places the initiation codon into the P site, where it directly base-pairs with eIF2-bound initiator methionyl transfer RNA to form a 48S initiation complex. However, all HCV-like IRESs also specifically interact with eIF3 (refs 2 , 5 , 6 , 7 , 9 , 10 , 11 , 12 ), but the role of this interaction in IRES-mediated initiation has remained unknown. During canonical initiation, eIF3 binds to the 40S subunit as a component of the 43S pre-initiation complex, and comparison of the ribosomal positions of eIF3 13 and the HCV IRES 8 revealed that they overlap, so that their rearrangement would be required for formation of ribosomal complexes containing both components 13 . Here we present a cryo-electron microscopy reconstruction of a 40S ribosomal complex containing eIF3 and the CSFV IRES. Remarkably, although the position and interactions of the CSFV IRES with the 40S subunit in this complex are simila