Positive-strand RNA virus genome replication organelles: structure, assembly, control.

Positive-strand RNA [(+)RNA] viruses include pandemic SARS-CoV-2, tumor-inducing hepatitis C virus, debilitating chikungunya virus (CHIKV), lethal encephalitis viruses, and many other major pathogens. (+)RNA viruses replicate their RNA genomes in virus-induced replication organelles (ROs) that also evolve new viral species and variants by recombination and mutation and are crucial virus control targets. Recent cryo-electron microscopy (cryo-EM) reveals that viral RNA replication proteins form striking ringed 'crowns' at RO vesicle junctions with the cytosol. These crowns direct RO vesicle formation, viral (-)RNA and (+)RNA synthesis and capping, innate immune escape, and transfer of progeny (+)RNA genomes into translation and encapsidation. Ongoing studies are illuminating crown assembly, sequential functions, host factor interactions, etc., with significant implications for control and beneficial uses of viruses.