title: Functional and structural analysis of the internal ribosome entry site present in the mRNA of natural variants of the HIV-1.
abstract: The 5'untranslated regions (UTR) of the full length mRNA of the HIV-1 proviral clones pNL4.3 and pLAI, harbor an internal ribosomal entry site (IRES). In this study we extend this finding by demonstrating that the mRNA 5'UTRs of natural variants of HIV-1 also exhibit IRES-activity. Cap-independent translational activity was demonstrated using bicistronic mRNAs in HeLa cells and in Xenopus laevis oocytes. The possibility that expression of the downstream cistron in these constructs was due to alternative splicing or to cryptic promoter activity was ruled out. The HIV-1 variants exhibited significant 5'UTR nucleotide diversity with respect to the control sequence recovered from pNL4.3. Interestingly, translational activity from the 5'UTR of some of the HIV-1 variants was enhanced relative to that observed for the 5'UTR of pNL4.3. In an attempt to explain these findings we probed the secondary structure of the variant HIV-1 5'UTRs using enzymatic and chemical approaches. Yet subsequent structural analyses did not reveal significant variations when compared to the pNL4.3-5'UTR. Thus, the increased IRES-activity observed for some of the HIV-1 variants cannot be ascribed to a specific structural modification. A model to explain these findings is proposed.
authors.affiliation: Laboratorio de Virología Molecular, Instituto Milenio de Inmunología e Inmunoterapia, Centro de Investigaciones Médicas, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Maricarmen
authors.initials: M
authors.lastname: Vallejos
authors.forename: Felipe
authors.initials: F
authors.lastname: Carvajal
authors.forename: Karla
authors.initials: K
authors.lastname: Pino
authors.forename: Camilo
authors.initials: C
authors.lastname: Navarrete
authors.forename: Marcela
authors.initials: M
authors.lastname: Ferres
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Huidobro-Toro
authors.forename: Bruno
authors.initials: B
authors.lastname: Sargueil
authors.forename: Marcelo
authors.initials: M
authors.lastname: López-Lastra
mesh_terms: D020121:5' Untranslated Regions; D015497:HIV-1 / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D012367:RNA, Viral / Q000097:blood; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D012333:RNA, Messenger; D012367:RNA, Viral