Rotavirus plus-strand RNAs not only direct protein synthesis but also serve as templates for the synthesis of the segmented double-stranded RNA (dsRNA) genome. In this study, we identified short-interfering RNAs (siRNAs) for viral genes 5, 8, and 9 that suppressed the expression of NSP1, a nonessential protein; NSP2, a component of viral replication factories (viroplasms); and VP7, an outer capsid protein, respectively. The loss of NSP2 expression inhibited viroplasm formation, genome replication, virion assembly, and synthesis of the other viral proteins. In contrast, the loss of VP7 expression had no effect on genome replication; instead, it inhibited only outer-capsid morphogenesis. Similarly, neither genome replication nor any other event of the viral life cycle was affected by the loss of NSP1. The data indicate that plus-strand RNAs templating dsRNA synthesis within viroplasms are not susceptible to siRNA-induced RNase degradation. In contrast, plus-strand RNAs templating protein synthesis in the cytosol are susceptible to degradation and thus are not the likely source of plus-strand RNAs for dsRNA synthesis in viroplasms. Indeed, immunofluorescence analysis of bromouridine (BrU)-labeled RNA made in infected cells provided evidence that plus-strand RNAs are synthesized within viroplasms. Furthermore, transfection of BrU-labeled viral plus-strand RNA into infected cells suggested that plus-strand RNAs introduced into the cytosol do not localize to viroplasms. From these results, we propose that plus-strand RNAs synthesized within viroplasms are the primary source of templates for genome replication and that trafficking pathways do not exist within the cytosol that transport plus-strand RNAs to viroplasms. The lack of such pathways confounds the development of reverse genetics systems for rotavirus.Rotaviruses, members of the Reoviridae, are an important cause of acute gastroenteritis in infants and young children (15). The virion is an icosahedron composed of three concentric layers of protein with a genome of 11 segments of doublestranded RNA (dsRNA) (30). The outer layer of the infectious triple-layered particle (TLP) is made up of the glycoprotein, VP7, and the spike protein, VP4. The intermediate layer is formed by VP6 trimers, and the inner layer is formed by the core lattice protein, VP2, arranged with Tϭ1 icosahedral symmetry. Positioned at the vertices of the VP2 lattice are individual copies of the RNA-dependent RNA polymerase (RdRp) VP1, and the mRNA-capping enzyme VP3. Together, VP1, VP2, VP3, and the dsRNA genome make up the core of the virion (19).Rotavirus entry is accompanied by the loss of the VP4 and VP7 outer layer, thereby converting TLPs to double-layered particles (DLPs). The RdRp of the DLP functions as a transcriptase to synthesize the 11 viral plus-strand RNAs (18). The plus-strand RNAs are extruded from DLPs through channels at the vertices that extend through both the VP2 and VP6 protein layers. The plus-strand RNAs contain 5Ј caps but lack 3Ј poly(A) tails and are translated to gi...

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Budding of Ebola virus (EBOV) particles from the plasma membrane of infected cells requires viral and host proteins. EBOV virus matrix protein VP40 recruits TSG101, an ESCRT-1 (host cell endosomal sorting complex required for transport-1) complex protein in the vacuolar protein sorting (vps) pathway, to the plasma membrane during budding. Involvement of other vps proteins in EBOV budding has not been established. Therefore, we used VP40 deletion analysis, virus-like particle-release assays, and confocal microscopy to investigate the potential role of ESCRT-1 proteins VPS4, VPS28, and VPS37B in EBOV budding. We found that VP40 could redirect each protein from endosomes to the cell surface independently of TSG101 interaction. A lack of VPS4 adenosine triphosphatase activity reduced budding by up to 80%. Inhibition of VPS4 gene expression by use of phosphorodiamidite morpholino antisense oligonucleotides protected mice from lethal EBOV infection. These data show that EBOV can use vps proteins independently of TSG101 for budding and reveal VPS4 as a potential target for filovirus therapeutics.