The 3' untranslated regions of Ebola virus mRNAs contain AU-rich elements involved in post-transcriptional stabilization and decay.

The 3' untranslated regions (UTRs) of Ebola virus (EBOV) mRNAs are enriched in their AU content and as such represent potential targets for RNA binding proteins targeting AU-rich elements (ARE-BPs). ARE-BPs are known to fine-tune RNA stability and translational activity, particularly of transiently expressed genes. We identified putative AREs within the 3' UTRs of EBOV nucleoprotein mRNAs and aimed to determine whether these regions are involved in modulating EBOV mRNA post-transcriptional stability as functional targets of ARE-BPs. Using reporter assays designed to study the function of 3' UTRs in mammalian cells and zebrafish embryos, we show that the tested EBOV 3' UTRs increase reporter activity, either through enhancing the stability or promoting the translation of reporter mRNA, and that this stabilizing effect is conserved across species. This effect was most pronounced for the nucleoprotein (NP) 3' UTR. When the EBOV 3' UTR reporter constructs were co-expressed with tristetraprolin (TTP, ZFP36), a prototypic ARE-BP that is known to mainly destabilize its target mRNAs, only the NP 3' UTR was responsive as shown by a decrease in reporter gene activity. Co-expression of EBOV NP with TTP led to downregulation of NP protein expression and reduced EBOV minigenome activity, which was dependent on the presence of the NP 3' UTR, indicating that TTP recognizes cis-acting elements within the NP 3' UTR. In conclusion, the enrichment of AU residues in EBOV 3' UTRs makes them possible targets for cellular ARE-BPs, leading to modulation of RNA stability and translational activity.