Ebola virus RNA editing:Characterization of the mechanism and gene products

Abstract

Ebola virus (EBOV) is an enveloped, negative-sense single-stranded RNA virus that causes severe hemorrhagic fever in humans and nonhuman primates. The EBOV glycoprotein (GP) gene encodes multiple transcripts due to RNA editing at a conserved editing site (ES) (a hepta-uridine stretche). The majority of GP gene transcript is unedited and encodes for a soluble glycoprotein (sGP); a defined function has not been assigned for sGP. In contrast, the transmembrane glycoprotein (GP1,2) dictates viral tropism and is expressed through RNA editing by insertion of a nontemplate adenosine (A) residue. Hypothetically, the insertion/deletion of a different number of A residues through RNA editing would result in another yet unidentified GP gene product, the small soluble glycoprotein (ssGP). I have shown that ssGP specific transcripts were indeed produced during EBOV infection. Detection of ssGP during infection was challenging due to the abundance of sGP over ssGP and the absence of distinguishing antibodies for ssGP. Optimized two- dimensional (2-D) gel electrophoresis verified the expression of ssGP during infection. Biophysical characterization revealed ssGP is a disulfide-linked homodimer that is exclusively N-glycosylated. Although ssGP appears to share similar structural properties with sGP, it does not have the same anti-inflammatory function. Using a new rapid transcript quantification assay (RTQA), I was able to demonstrate that RNA editing is an inherent feature of the genus Ebolavirus and all species of EBOV produce multiple GP gene products. A newly developed dual-reporter minigenome system was utilized to characterize EBOV RNA editing and determined the conserved ES sequence and cis-acting sequences as primary and secondary requirements for RNA editing, respectively. Viral protein (VP) 30, a transcription activator, was identified as a contributing factor of RNA editing— a proposed novel function for this largely uncharacterized viral protein. Finally, I could show that EBOV RNA editing is GP gene-specific because a similar sequence located in L gene did not serve as an ES, most likely due to the lack of the necessary cis-acting sequences. In conclusion, I identified a novel soluble protein of EBOV whose function needs further characterization. I also shed light into the mechanism of EBOV RNA editing, a potential novel target for intervention.