Virus Factories and Mini-Organelles Generated for Virus Replication

Mammalian orthoreovirus core protein μ2 reorganizes host microtubule-organizing center components

Filamentous mammalian orthoreovirus (MRV) viral factories (VFs) are membrane-less cytosolic inclusions in which virus transcription, replication of dsRNA genome segments, and packaging of virus progeny into newly synthesized virus cores take place. In infected cells, the MRV μ2 protein forms punctae in the enlarged region of the filamentous VFs that are co-localized with γ-tubulin and resistant to nocodazole treatment, and permitted microtubule (MT)-extension, features common to MT-organizing centers (MTOCs). Using a previously established reconstituted VF model, we addressed the functions of MT-components and MTOCs concerning their roles in the formation of filamentous VFs. Indeed, the MTOC markers γ-tubulin and centrin were redistributed within the VF-like structures (VFLS) in a μ2-dependent manner. Moreover, the MT-nucleation centers significantly increased in numbers, and γ-tubulin was pulled-down in a binding assay when co-expressed with histidine-tagged-μ2 and μNS. Thus, μ2, by interaction with γ-tubulin, can modulate MTOCs localization and function according to viral needs.