title: Evidence for an RNA chaperone function of polypyrimidine tract-binding protein in picornavirus translation.
abstract: The cellular polypyrimidine tract-binding protein (PTB) is recruited by the genomic RNAs of picornaviruses to stimulate translation initiation at their internal ribosome entry site (IRES) elements. We investigated the contribution of the individual RNA recognition motif (RRM) domains of PTB to its interaction with the IRES of foot-and-mouth disease virus (FMDV). Using a native gel system, we found that PTB is a monomer, confirming recent reports that challenged the previous view that PTB is a dimer. Mapping the spatial orientation of PTB relative to the bound IRES RNA, we found that the two C-terminal RRM domains III and IV of PTB bind in an oriented way to the IRES. Domain III contacts the IRES stem-loop 2, while domain IV contacts the separate IRES 3' region. PTB domain I appears not to be involved directly in RNA binding, but domain II stabilizes the RNA binding conferred by domains III and IV. A PTB protein containing only these two C-terminal PTB domains is sufficient to enhance the entry of initiation factor eIF4G to the IRES and stimulate IRES activity, and the long-lived PTB-IRES interaction stabilized by domain II is not a prerequisite for this function. Thus, PTB most likely acts as an RNA chaperone to stabilize IRES structure and, in that way, augment IRES activity.
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, 35392 Giessen, Germany.
authors.forename: Yutong
authors.initials: Y
authors.lastname: Song
authors.forename: Eleni
authors.initials: E
authors.lastname: Tzima
authors.forename: Kerstin
authors.initials: K
authors.lastname: Ochs
authors.forename: Gergis
authors.initials: G
authors.lastname: Bassili
authors.forename: Heidi
authors.initials: H
authors.lastname: Trusheim
authors.forename: Monica
authors.initials: M
authors.lastname: Linder
authors.forename: Klaus T
authors.initials: KT
authors.lastname: Preissner
authors.forename: Michael
authors.initials: M
authors.lastname: Niepmann
mesh_terms: D005537:Aphthovirus / Q000378:metabolism; D001665:Binding Sites; D024202:Electrophoretic Mobility Shift Assay; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D010849:Picornaviridae / Q000235:genetics / Q000378:metabolism*; D038941:Polypyrimidine Tract-Binding Protein / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D039603:Eukaryotic Initiation Factor-4G; D018832:Molecular Chaperones; D012367:RNA, Viral; D038941:Polypyrimidine Tract-Binding Protein