| Positive-strand RNA [(+)RNA] viruses, whose virions contain messenger sense, single stranded RNA, compose over one-third of known virus genuses. (+)RNA viruses replicate their genome through negative-strand RNA intermediates and all known (+)RNA viruses replicate their RNA on intracellular membranes in association with vesicles or other membrane alterations. Despite its necessity in viral replication, the membrane involvement in viral RNA-dependent RNA synthesis remains poorly understood. As a highly conserved process in the viral life cycle, RNA replication is a valuable target for developing antiviral drugs. Brome mosaic virus (BMV) is an advantageous system to study some of the common features of replication by numerous positive-strand RNA viruses. Previous studies with BMV have shown that the genome replication complexes of (+)RNA viruses, reverse transcribing viruses, and double-stranded RNA viruses share structural, functional and likely evolutionary links. Here, we tested and refined a proposed model for (+)RNA viral replication complex formation, structure, and organization using a yeast model system. Among other things, we showed that host factors are crucially involved in stabilizing and maintaining the BMV-induced membrane-bound replication compartments. Moreover, the observations presented here are consistent with a model for which multimerization and intramolecular interactions between the capping and helicase-like domains of BMVs 1 a protein are required for several different steps of BMV replication, from RNA recruitment and RNA replication to replication compartment formation. The insights obtained from this work appear relevant to many other (+)RNA viruses as these and other results suggest that seemingly diverse membrane rearrangements may represent topologically and functionally related structures. |
