Interaction of Bunyamwera Virus Non-Structural Protein NSm with Cellular BNIP1 is Required for Efficient Viral Gene Expression and Replication

Bunyamwera virus (BUNV) is the prototypical member of the Peribunyaviridae family of arthropod-borne viruses and possesses a genome comprising three segments of negative-sense RNA, named small, medium and large. The medium segment encodes a polyprotein that is processed to form Gn and Gc spikes and a non-structural protein, NSm. The role of NSm during replication in mammalian cells is poorly characterized, although it associates with a Golgi-derived structure called the virus factory (VF), the site of BUNV genome replication and virion assembly. To further define NSm function, we generated an epitope-tagged BUNV and used co-immunoprecipitation and quantitative proteomics to identify host interacting partners. NSm interacted with BCL-2 interacting protein 1 (BNIP1), a SNARE protein involved in COPI vesicle trafficking, with the importance of this interaction demonstrated by siRNA-mediated knockdown of BNIP1 expression, which significantly reduced BUNV gene expression and virion production. Interestingly, NSm also interacted with components of the NRZ complex, involved in COPI vesicle tethering in association with BNIP1, and inhibition of COPI complex formation resulted in loss of NSm expression. Taken together, our results identify BNIP1 as a host cell factor necessary for efficient BUNV replication and suggest the cellular localization of NSm at the VF is COPI-dependent.