Virus factories, double membrane vesicles and viroplasm generated in animal cells

Highlights ► Assembly of replicase proteins of (+) strand RNA virus occurs on the cytoplasmic face of membrane-bound organelles. ► Replicase assembly leads to membrane invaginations called spherules or double membraned vesicles. ► Replicase assembly can be facilitated by Arf1 dependent recruitment of phosphatidylinositol-4-kinase-III. ► Large DNA viruses replicate and/or assemble in perinuclear factories that resemble cellular aggresomes generated in response to protein aggregation. ► Virus factories segregate viral DNA and RNA and appear to be distinct entities within the cell.
Many viruses reorganise cellular membrane compartments and the cytoskeleton to generate subcellular microenvironments called virus factories or ‘viroplasm’. These create a platform to concentrate replicase proteins, virus genomes and host proteins required for replication and also protect against antiviral defences. There is growing interest in understanding how viruses induce such large changes in cellular organisation, and recent studies are beginning to reveal the relationship between virus factories and viroplasm and the cellular structures that house them. In this review, we discuss how three supergroups of (+)RNA viruses generate replication sites from membrane-bound organelles and highlight research on perinuclear factories induced by the nucleocytoplasmic large DNA viruses.