Plays an essential role in viral RNA synthesis and also a role in suppressing innate immune signaling. Acts as a polymerase cofactor in the RNA polymerase transcription and replication complexes (By similarity). Serves as nucleoprotein/NP monomer chaperone prior to the formation of the large oligomeric RNA-bound complexes (PubMed:31337716). Regulates RNA synthesis by modulating NP-RNA interactions and interacting with DYNLL1. VP35-NP interaction controls the switch between RNA-bound NP and free NP and thus the switch between genome replication and genome packaging into the nucleocapsid. Prevents establishment of cellular antiviral state, thereby suppressing host DC maturation. Acts by inhibiting host DDX58/RIG-I activation both by shielding dsRNA from detection and by preventing PRKRA binding to DDX58. Blocks virus-induced phosphorylation and activation of interferon regulatory factor 3/IRF3, a transcription factor critical for the induction of interferons alpha and beta. This blockage is produced through the interaction with and inhibition of host IKBKE and TBK1, producing a strong inhibition of the phosphorylation and activation of IRF3. Also inhibits the antiviral effect mediated by the host interferon-induced, double-stranded RNA-activated protein kinase EIF2AK2/PKR. Increases PIAS1-mediated SUMOylation of IRF7, thereby repressing interferon transcription (By similarity). Also acts as a suppressor of RNA silencing by interacting with host DICER1, TARBP2/TRBP and PRKRA/PACT (By similarity). As a dimer, binds and sequesters dsRNA contributing to the inhibition of interferon production (By similarity). Homodimer (By similarity). Homooligomer; via the coiled coil domain. Interacts with nucleoprotein NP and polymerase L; VP35 bridges L and NP and allows the formation of the polymerase complex (Probable). Also interacts with VP30; this interaction is regulated by VP30 phosphorylation. Interacts with host IKBKE and TBK1; the interactions lead to inhibition of cellular antiviral response by blocking necessary interactions of IKBKE and TBK1 with their substrate IRF3. Interacts with host DYNLL1; this interaction stabilizes VP35 N-terminal oligomerization domain, enhances viral RNA synthesis but does not participate in suppressing the host innate immune response. Interacts with host PRKRA; this interaction inhibits the interaction between DDX58 and PRKRA. Interacts with dsRNA. Interacts with host TRIM6; this interaction plays an important role in promoting efficient viral replication. Interacts with host STAU1. Interacts with host IRF7, PIAS1 and UBE2I/UBC9; these interactions mediate the sumoylation of IRF7 and contribute to the inhibition of IFN-type I production (By similarity). Interacts with host DICER1; this interaction prevents TARBP2/TRBP binding to DICER1 and thus allows the virus to counteract host RNA silencing. Interacts with host TARBP2/TRBP and PRKRA/PACT; these interactions prevent TARBP2 and PRKRA binding to DICER1 and thus allows the virus to counteract host RNA silencing (By similarity). Phosphorylated by host IKBKE. Phosphorylation contributes to efficient viral replication and transcription. Belongs to the filoviridae polymerase cofactor VP35 family.