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bioRxiv · 10.1101/2022.08.25.505333

Structural insights into viral genome replication by the Severe fever with thrombocytopenia syndrome virus L protein

Williams, H. M.·Thorkelsson, S. R.·Vogel, D.·Milewski, M.·Busch, C.·Cusack, S.·Grunewald, K.·Quemin, E.·Rosenthal, M.
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Abstract

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a phenuivirus that has rapidly become endemic in several East Asian countries. The large (L) protein of SFTSV, which includes the RNA-dependent RNA polymerase (RdRp), is responsible for catalysing viral genome replication and transcription. Here, we present 5 cryo-electron microscopy (cryo-EM) structures of the L protein in several states of the genome replication process, from pre-initiation to late-stage elongation, at a resolution of up to 2.6 [A]. We identify how the L protein binds the 5' viral RNA in a hook-like conformation and show how the distal 5' and 3' RNA ends form a duplex positioning the 3' RNA terminus in the RdRp active site ready for initiation. We also observe the L protein stalled in the early- and late-stages of elongation with the RdRp core accommodating a 9-bp product-template duplex. This duplex ultimately splits with the template binding to a designated 3' secondary binding site. The structural data and observations are complemented by in vitro biochemical and cell-based mini-replicon assays. Altogether, our data provide novel key insights into the mechanism of viral genome replication by the SFTSV L protein and will aid drug development against segmented negative-strand RNA viruses.

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Williams, H. M., Thorkelsson, S. R., Vogel, D., Milewski, M., Busch, C., Cusack, S., Grunewald, K., Quemin, E., Rosenthal, M.. 2022-08-26. Structural insights into viral genome replication by the Severe fever with thrombocytopenia syndrome virus L protein. https://doi.org/10.1101/2022.08.25.505333

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