The 5′ UTR of HIV-1 full-length mRNA and the Tat viral protein modulate the programmed −1 ribosomal frameshift that generates HIV-1 enzymes
- 1Département de biochimie, Université de Montréal, Montréal, Québec, Canada, H3T 1J4
- 2Centre de recherche, Hôpital Ste-Justine, Montréal, Québec, Canada, H3T 1C5
Abstract
Translation of the full-length messenger RNA (mRNA) of the human immunodeficiency virus type 1 (HIV-1) generates the precursor of the viral enzymes via a programmed −1 ribosomal frameshift. Here, using dual-luciferase reporters, we investigated whether the highly structured 5′ untranslated region (UTR) of this mRNA, which interferes with translation initiation, can modulate HIV-1 frameshift efficiency. We showed that, when the 5′ UTR of HIV-1 mRNA occupies the 5′ end of the reporter mRNA, HIV-1 frameshift efficiency is increased about fourfold in Jurkat T-cells, compared with a control dual-luciferase reporter with a short unstructured 5′ UTR. This increase was related to an interference with cap-dependent translation initiation by the TAR-Poly(A) region at the 5′ end of the messenger. HIV-1 mRNA 5′ UTR also contains an internal ribosome entry site (IRES), but we showed that, when the cap-dependent initiation mode is available, the IRES is not used or is weakly used. However, when the ribosomes have to use the IRES to translate the dual-luciferase reporter, the frameshift efficiency is comparable to that of the control dual-luciferase reporter. The decrease in cap-dependent initiation and the accompanying increase in frameshift efficiency caused by the 5′ UTR of HIV-1 mRNA is antagonized, in a dose-dependent way, by the Tat viral protein. Tat also stimulates the IRES-dependent initiation and decreases the corresponding frameshift efficiency. A model is presented that accounts for the variations in frameshift efficiency depending on the 5′ UTR and the presence of Tat, and it is proposed that a range of frameshift efficiencies is compatible with the virus replication.
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Footnotes
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↵3 Corresponding authors.
E-mail lea.brakier.gingras{at}umontreal.ca.
E-mail g.ferbeyre{at}umontreal.ca.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.030346.111.
- Received September 13, 2011.
- Accepted December 1, 2011.
- Copyright © 2012 RNA Society