Functional interactomes of the Ebola virus polymerase identified by proximity proteomics in the context of viral replication

Ebola virus (EBOV) critically depends on the viral polymerase to replicate and transcribe the viral RNA genome. To examine whether interactions between EBOV polymerase and cellular and viral factors affect distinct viral RNA synthesis events, we applied proximity proteomics to define the cellular interactome of EBOV polymerase, under conditions that recapitulate viral transcription and replication. We engineered EBOV polymerase tagged with the split-biotin ligase split-TurboID, which successfully biotinylated the proximal proteome while retaining polymerase activity. We further analyzed the interactomes in an siRNA-based, functional screen and uncovered 35 host factors, which, when depleted, affect EBOV infection. We validated one host factor, eukaryotic peptide chain release factor subunit 3a (eRF3a/GSPT1), which we show physically and functionally associates with EBOV polymerase to facilitate viral transcription termination. Our work demonstrates the utility of proximity proteomics to capture the functional host-interactome of the EBOV polymerase and to illuminate host-dependent regulations of viral RNA synthesis.