The stress granule protein G3BP1 mediates norovirus VPg-dependent translation through eIF4GI-mediated interactions

Liliana Echavarria-Consuegra, University of Cambridge

Liliana Echavarria-Consuegra, Ian Goodfellow Division of Virology, Department of Pathology, University of Cambridge, Cambridge, United Kingdom

Entry and Replication

To enable translation of the viral genome, noroviruses highjack the host cell translation machinery via the virus-encoded protein VPg, which is covalently linked to the 5' end of the viral RNA. We have previously shown that VPg drives norovirus translation initiation via interactions with the cellular translation initiation factor eIF4G. Using orthogonal unbiased approaches, we demonstrated that VPg-mediated translation of both human and murine norovirus (MNV1) is dependant on the core stress granule component G3BP Stress Granule Assembly Factor 1 (G3BP1). To better characterise the relationship between G3BP1 and VPg, and to gain further insights into the mechanism underlying norovirus translation, we explored the ability of noroviruses to overcome a lack of G3BP1 via adaptation. Therefore, we generated G3BP1-independent MNV1 variants by serial passaging in ΔG3BP1 cells. Using nanopore sequencing we identified that mutations in the adapted virus accumulated in the C-terminal region of VPg that interacts with eIF4G. We confirmed that these mutations increased virus replication in the absence of G3BP1. Co-immunoprecipitation experiments revealed that some of the mutations are able to restore the VPg and eIF4G interaction when G3BP1 is ablated. In conclusion, we show that MNV1 adapts to the absence of G3BP1 in cell culture, bypassing its function in viral protein translation and therefore production of viral progeny. These results further corroborate the importance of the C-terminal region of VPg to drive viral genome expression, and give more insight into the role that G3BP1 plays in the stabilization of the translation initiation complex for ribosome recruitment.