Reovirus low-density particles package viral and cellular RNA

Packaging of segmented, double-stranded RNA viral genomes requires coordination of multiple 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. However, despite ostensibly lacking the genome, top component particles maintain a low level of infectivity. Whether reovirus particles can package host RNA is unknown. To gain insight into reovirus packaging potential and mechanisms, we employed next-generation RNA-sequencing to define the viral and host RNA content of purified reovirus virions and top component particles. Reovirus top component particles contained double-stranded viral RNA segments in similar proportions but at reduced levels compared to virions. Top component particles also were enriched for numerous host RNAs, especially short, non-polyadenylated transcripts, that differed by reovirus strain, independent of the viral polymerase. In contrast, virions were enriched for very few host RNAs. Collectively, these findings indicate that genome packaging into reovirus virions is exquisitely selective, while incorporation of host RNAs into top component particles is more promiscuous or differentially selective and may contribute to or result from inefficient viral RNA packaging. Overall design: Examination of RNA component in the Top component of reovirus