title: Initiation on the divergent Type I cadicivirus IRES: factor requirements and interactions with the translation apparatus.
abstract: Cadicivirus (CDV) is unique amongst picornaviruses in having a dicistronic genome with internal ribosomal entry sites (IRESs) preceding both open reading frames. Here, we investigated initiation on the 5'-terminal IRES. We report that the 982-nt long 5'UTR comprises 12 domains (d1-d12), five of which (d8-d12, nts 341-950) constitute a divergent Type I IRES. It comprises central elements (the apex of d10, d11 and the following polypyrimidine tract) that are homologous to corresponding elements in canonical Type 1 IRESs, and non-canonical flanking domains (d8, d9 and d12). In vitro reconstitution revealed that as with canonical Type I IRESs, 48S complex formation requires eukaryotic initiation factors (eIFs) 1, 1A, 2, 3, 4A, 4B and 4G, and the poly(C) binding protein 2 (PCBP2), and starts with specific binding of eIF4G/eIF4A to d11. However, in contrast to canonical Type I IRESs, subsequent recruitment of 43S ribosomal complexes does not require direct interaction of their eIF3 constituent with the IRES-bound eIF4G. On the other hand, the CDV IRES forms a 40S/eIF3/IRES ternary complex, with multiple points of contact. These additional interactions with translational components could potentially stimulate recruitment of the 43S complex and alleviate the necessity for direct eIF4G/eIF3 interaction.
authors.affiliation: Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC44, Brooklyn, NY 11203, USA.
authors.forename: Mukta
authors.initials: M
authors.lastname: Asnani
authors.affiliation: Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC44, Brooklyn, NY 11203, USA.
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Pestova
authors.affiliation: Department of Cell Biology, SUNY Downstate Medical Center, 450 Clarkson Avenue, MSC44, Brooklyn, NY 11203, USA christopher.hellen@downstate.edu.
authors.forename: Christopher U T
authors.initials: CU
authors.lastname: Hellen
mesh_terms: D020121:5' Untranslated Regions; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism; D039601:Eukaryotic Initiation Factor-4A / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D009154:Mutation; D010442:Peptide Chain Initiation, Translational; D010849:Picornaviridae / Q000235:genetics*; D012367:RNA, Viral / Q000737:chemistry* / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D039621:Eukaryotic Initiation Factor-3; D039603:Eukaryotic Initiation Factor-4G; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D039601:Eukaryotic Initiation Factor-4A