Regulation of Tacaribe mammarenavirus translation: Positive 5' and negative 3' elements and role of key cellular factors

FOSCALDI, SABRINA; D'ANTUONO, ALEJANDRA; NOVAL, MARÍA GABRIELA; GAY, GONZALO DE PRAT; SCOLARO, LUIS; LOPEZ, NORA

JOURNAL OF VIROLOGY

AMER SOC MICROBIOLOGY

Año: 2017 vol. 91

0022-538X

Mammarenaviruses are enveloped viruses with a bisegmented negativestranded 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 mRNAs 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 and transcripts bearing modified 5´ and/or 3´ UTR were evaluated in a cellbased 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,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 less impact on virus-like mRNA translation than on 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 noncanonical host factors for a cap-dependent initiation mechanism.