Reovirus Low-Density Particles Package Cellular RNA.

Timothy W Thoner,Xiang Ye,Kristen M Ogden,John Karijolich

doi:10.3390/v13061096

Abstract

Packaging of segmented, double-stranded RNA viral genomes requires coordination of viral proteins and RNA segments. For mammalian orthoreovirus (reovirus), evidence suggests either all ten or zero viral RNA segments are simultaneously packaged in a highly coordinated process hypothesized to exclude host RNA. Accordingly, reovirus generates genome-containing virions and “genomeless” top component particles. Whether reovirus virions or top component particles package host RNA is unknown. To gain insight into reovirus packaging potential and mechanisms, we employed next-generation RNA-sequencing to define the RNA content of enriched reovirus particles. Reovirus virions exclusively packaged viral double-stranded RNA. In contrast, reovirus top component particles contained similar proportions but reduced amounts of viral double-stranded RNA and were selectively enriched for numerous host RNA species, especially short, non-polyadenylated transcripts. Host RNA selection was not dependent on RNA abundance in the cell, and specifically enriched host RNAs varied for two reovirus strains and were not selected solely by the viral RNA polymerase. Collectively, these findings indicate that genome packaging into reovirus virions is exquisitely selective, while incorporation of host RNAs into top component particles is differentially selective and may contribute to or result from inefficient viral RNA packaging.

Highlights

Packaging of segmented, double-stranded RNA genomes by eukaryotic viruses is an incompletely understood process that requires the coordination of up to 12 viral RNA species as well as structural and non-structural proteins [1,2,3,4]
While the precise features of host RNA that facilitate packaging into top component (TC) particles remain to be elucidated, these findings suggest that genome packaging into reovirus virions is exquisitely selective, while RNA packaging into reovirus
To verify that TC particles are infectious, we enriched for recombinant strain Type 1 Lang (T1L) reovirus virions and TC particles by organic extraction and cesium chloride gradient ultracentrifugation from infected L cells. rsT1L TC could be cleanly separated from virions based on density (Figure 1A)

Summary

Introduction

Double-stranded RNA (dsRNA) genomes by eukaryotic viruses is an incompletely understood process that requires the coordination of up to 12 viral RNA species as well as structural and non-structural proteins [1,2,3,4]. Two major packaging models have been proposed: (i) a concerted model in which trans-interactions between plus-strand (+) RNA species of each segment promote formation of a packageable supramolecular complex that is subsequently encapsidated by viral structural proteins, and (ii) a core-filling model wherein each segment is individually packaged into a preformed core particle [1,2]. Following viral +RNA packaging, minus-strand RNA is synthesized to form dsRNA genome segments, which are present in particles in equimolar proportions. Many questions about how these viruses package their multi-partite genomes remain unanswered

Methods

Results

Conclusion