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UBC Theses and Dissertations

Anatomy of an RNA virus : dissecting the host-virus interactions that govern dicistrovirus gene expression and transmission Kerr, Craig Howard


Viruses exist as obligate intracellular parasites, with one of the largest classifications of viruses being the positive single stranded RNA viruses ((+)ssRNA). Viral families in this group are incredibly diverse in their replication schemes and host tropisms. Despite this, there exist fundamental principles between them. Unravelling these common mechanisms can give rise to a greater understanding of virus biology and lead to the development of novel antiviral therapies and biotechnology. Members of the Dicistroviridae contain monopartite, (+)ssRNA genomes, between 8 to 10 kilobases in size. Infectious to agriculturally and economically important arthropods, these viruses have served as model systems to study fundamental cellular processes such as translation and innate immunity. Dicistroviruses contain two open reading frames (ORFs), which are translated by two distinct internal ribosome entry sites (IRESs). The 5’ untranslated region IRES drives translation of the viral non-structural proteins encoded in ORF1, whereas the intergenic region (IGR) IRES directs translation of the viral structural proteins of ORF2. The scheme by which these viruses replicate is poorly described. Here, we develop the first infectious clones of the dicistrovirus type species, Cricket paralysis virus (CrPV), termed CrPV-2 and -3. We demonstrate that this clone is fully infectious in Drosophila S2 cells and causes mortality when injected into adult flies. Utilizing this clone, we examined how specific mutations in the IGR IRES affect viral gene expression in vivo. Moreover, we demonstrate that the CrPV IGR IRES uses an unusual mechanism for +1-frame translation of a hidden overlapping ORF, which is important for viral pathogenesis. Finally, using a combination of biochemical and mass spectrometry based approaches we show that CrPV may usurp cellular pathways to obtain an envelope. This thesis offers insights into the complex replication scheme of dicistroviruses and provides a foundation for future studies into the life cycle of these viruses.

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