title: Cap-independent translation of tobacco etch virus is conferred by an RNA pseudoknot in the 5'-leader.
abstract: The tobacco etch virus (TEV) 5'-leader promotes cap-independent translation in a 5'-proximal position and promotes internal initiation when present in the intercistronic region of a dicistronic mRNA, indicating that the leader contains an internal ribosome entry site. The TEV 143-nucleotide 5'-leader folds into a structure that contains two domains, each of which contains an RNA pseudoknot. Mutational analysis of the TEV 5'-leader identified pseudoknot (PK) 1 within the 5'-proximal domain and an upstream single-stranded region flanking PK1 as necessary to promote cap-independent translation. Mutations to either stem or to loops 2 or 3 of PK1 substantially disrupted cap-independent translation. The sequence of loop 3 in PK1 is complementary to a region in 18 S rRNA that is conserved throughout eukaryotes. Mutations within L3 that disrupted its potential base pairing with 18 S rRNA reduced cap-independent translation, whereas mutations that maintained the potential for base pairing with 18 S rRNA had little effect. These results indicated that the TEV 5'-leader functionally substitutes for a 5'-cap and promotes cap-independent translation through a 45-nucleotide pseudoknot-containing domain.
authors.affiliation: Department of Biochemistry, University of California, Riverside, California 92521-0129, USA.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Zeenko
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gallie
mesh_terms: D020029:Base Pairing; D017124:Conserved Sequence; D021901:DNA, Intergenic; D004279:DNA, Viral / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D010942:Plant Viruses / Q000235:genetics / Q000502:physiology*; D014176:Protein Biosynthesis; D012315:RNA Caps; D012333:RNA, Messenger / Q000737:chemistry* / Q000235:genetics*; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics; D014026:Nicotiana / Q000821:virology*
chemical_list: D021901:DNA, Intergenic; D004279:DNA, Viral; D012315:RNA Caps; D012333:RNA, Messenger; D012337:RNA, Ribosomal, 18S; D012367:RNA, Viral