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Regulation of Tacaribe Mammarenavirus Translation: Positive 5' and Negative 3' Elements, and Role of Key Cellular Factors.

J Virol; 2017 May 03.
Artículo en Inglés | MEDLINE | ID: mdl-28468879

Resumen

Mammarenaviruses are enveloped viruses with a bisegmented negative-stranded RNA genome that encodes the nucleocapsid protein (NP), the envelope glycoprotein precursor (GPC), the RNA polymerase (L), and a RING matrix protein (Z). Viral proteins are synthesized from subgenomic messenger RNAs bearing a capped 5' untranslated region (UTR), and lacking 3' poly(A) tail. We analyzed the translation strategy of Tacaribe virus (TCRV), a prototype of the New World mammarenaviruses. A virus-like transcript that carries a reporter gene in place of the NP open-reading frame as well as transcripts bearing modified 5' and/or 3' UTRs were evaluated in a cell-based translation assay. We found that the presence of the cap structure at the 5' end dramatically increases translation efficiency, and that the viral 5' UTR comprises stimulatory signals while the 3' UTR, and specifically the presence of a terminal C+G-rich sequence and/or a stem-loop structure, down-modulates translation. Additionally, translation was profoundly reduced in eukaryotic initiation factor (eIF) 4G-inactivated cells, whereas depletion of intracellular levels of eIF4E had lesser impact on virus-like mRNA translation, as compared with a cell-like transcript. Translation efficiency was independent of NP expression or TCRV infection. Our results indicate that TCRV mRNAs are translated using a cap-dependent mechanism, whose efficiency relies on the interplay between stimulatory signals in the 5' UTR and a negative modulatory element in the 3' UTR. The low dependence on eIF4E suggests that viral mRNAs may engage yet unknown non-canonical host factors for a cap-dependent initiation mechanism. Several members of the family cause serious hemorrhagic fevers in humans. In the present report, we describe the mechanism by which Tacaribe virus, a prototypic non-pathogenic NW mammarenavirus, regulates viral mRNA translation. Our results highlight the impact of untranslated sequences and key host translation factors on this process. We propose a model that explains how viral mRNAs outcompete cellular mRNAs for the translation machinery. A better understanding of the mechanism of translation regulation of this virus can provide the bases for the rational design of new antiviral tools directed to pathogenic arenaviruses.