Visualisation of the bunyavirus RNA synthesis machinery in action

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The Bunyavirales order of segmented negative sense RNA viruses comprises some of themost serious human pathogens in existence, including 3 listed by the World HealthOrganisation as priority pathogens. Their RNA genome associates with two proteins,nucleoprotein (NP) and RNA dependent RNA polymerase (RdRp) to form aribonucleoprotein complex (RNP); this complex is the bunyaviral RNA synthesismachinery. Previous work demonstrated the RNP complex has inherent flexibility,resulting in conflicting models describing RNP structure. However, our recent work hasallowed us to structurally characterise the Bunyamwera virus (BUNV) RNP, by using avariety of microscopy approaches, including negative staining electron microscopy, cryoelectrontomography and atomic force microscopy (1). This work demonstrated that theBUNV RNP presents a helical architecture of the RNP and allowed an atomic model to begenerated for the nucleoprotein (NP) arrangement, which in turn allowed NP residuescritical for the formation of active RNP to be identified. However, these findings also raisedmany questions. For example, why are BUNV RNPs loose helices? What is themechanism responsible for circularising BUNV RNPs? Why is the RdRp not usuallyobserved on BUNV RNPs and what is the structure of the RdRp within the RNParchitecture? How representative is this model of other bunyavirus RNPs?This project will build upon this work through investigating the RNPs of members of theArenaviridae. Members of this family contain human pathogens which are the causativeagents of haemorrhagic fever and therapeutic options for such pathogens are limited.Specifically, the RNP of lymphocytic choriomeningitis virus (LCMV) will be investigated, asa representative member of the family. The project will aim to determine the structure ofthe LCMV RNP (following a similar approach to that employed for BUNV RNP), determinethe structure of the LCMV RdRp within the RNP complex, image native RNP's undergoingRNA synthesis and investigate the RNP complex within LCMV viral factories.1 - Hopkins FR, Álvarez-Rodriguez B, Heath GR, Panayi K, Hover S, Edwards TA, BarrJN, Fontana J. 2022. The Native Orthobunyavirus Ribonucleoprotein Possesses a HelicalArchitecture. mBio. https://doi.org/10.1128/mbio.01405-22