VPg of murine norovirus binds translation initiation factors in infected cells

Background: Norovirus genomic and subgenomic RNAs are covalently linked at the 5' nucleotide to a 15 kD protein called VPg. VPg of two human norovirus strains binds translation initiation factor eIF3 and other eIFs in vitro, suggesting VPg functions in initiation of protein synthesis on viral RNA. Human norovirus strains are not cultivable, and thus experimental evidence of interactions between VPg and eIFs in infected cells has been lacking. We used the cultivable murine norovirus MNV-I as a model to study interactions between VPg and eIFs in infected cells. Results: As shown previously for human norovirus VPg, MNV-I VPg bound eIF3, eIF4GI, eIF4E, and S6 ribosomal protein in cell extracts by GST pull-down assay. Importantly, MNV-I VPg co-precipitated eIF4GI and eIF4E from infected macrophages, providing evidence that VPg interacts with components of the translation machinery in norovirus infected cells. Conclusion: The interactions between MNV-I VPg and eIFs completely mimic those reported for the human norovirus VPg, illustrating the utility of MNV-I as a relevant molecular model to study mechanisms of human norovirus replication.