Asymmetric reconstruction of mammalian reovirus reveals interactions among RNA, transcriptional factor μ2 and capsid proteins

Mammalian reovirus (MRV) is a double-stranded RNA (dsRNA) virus that affects the gastrointestinal and respiratory tracts. Here, the authors present the 3.3 angstrom cryo-EM asymmetric reconstruction of transcribing MRV that reveals the organization of the dsRNA genome, RNA interaction with the polymerase complex, and how the polymerase interacts extensively with its co-factor, mu 2, to form a transcription enzyme complex, which engages and regulates RNA transcription. Mammalian reovirus (MRV) is the prototypical member of genus Orthoreovirus of family Reoviridae. However, lacking high-resolution structures of its RNA polymerase cofactor mu 2 and infectious particle, limits understanding of molecular interactions among proteins and RNA, and their contributions to virion assembly and RNA transcription. Here, we report the 3.3 angstrom-resolution asymmetric reconstruction of transcribing MRV and in situ atomic models of its capsid proteins, the asymmetrically attached RNA-dependent RNA polymerase (RdRp) lambda 3, and RdRp-bound nucleoside triphosphatase mu 2 with a unique RNA-binding domain. We reveal molecular interactions among virion proteins and genomic and messenger RNA. Polymerase complexes in three Spinoreovirinae subfamily members are organized with different pseudo-D-3d symmetries to engage their highly diversified genomes. The above interactions and those between symmetry-mismatched receptor-binding sigma 1 trimers and RNA-capping lambda 2 pentamers balance competing needs of capsid assembly, external protein removal, and allosteric triggering of endogenous RNA transcription, before, during and after infection, respectively.

Automated summary

The authors presented a 3.3 angstrom cryo-EM asymmetric reconstruction of transcribing MRV, revealing molecular interactions among virion proteins and genomic and messenger RNA. The study helps to understand the molecular mechanisms involved in virus assembly and RNA transcription by elucidating different interactions among molecules.