Architecture and biogenesis of plus-strand RNA virus replication factories

Figure 2 Topology of plus-strand RNA virus replication sites. A: RNA replication of plus-strand RNA viruses inducing invaginated vesicles/spherules is thought to occur in the spherule lumen. Examples of viruses inducing this type of remodeled membranes are denoted. The neck like opening to the cytoplasm allows export of progeny RNA destined for translation or packaging, as well as import of metabolites required for RNA replication; B: Possible topologies of RNA replication site for double membrane vesicle (DMV)-type factories. Enterovirus replication is thought to take place on the outer membrane of single membrane tubules and DMVs, whereas the exact replication site of nidovirales and hepatitis C virus (HCV) is still unclear as indicated by the question marks. Replication in the DMV lumen would require import and export across two membranes, which could be mediated via a proteinacous transport complex, or via an opening to the cytosol of not yet fully closed DMVs (see main text for details). SFV: Semliki Forrest virus; SINV: Sindbis virus; RUBV: Rubella virus; BMV: Brome mosaic virus; FHV: Flock-house virus; DENV: Dengue virus; WNV: West Nile virus; PV: Poliovirus; CVB3: Coxsackievirus B3; SARS-CoV: Severe acute respiratory syndrome coronavirus; MHV: Mouse hepatitis virus; EAV: Equine arterivirus.