Displays RNA-directed RNA polymerase, deubiquitinating and deISGylase activities (PubMed:18078692, PubMed:21228232, PubMed:21245344, PubMed:23345508). RNA-dependent RNA polymerase is responsible for replication and transcription of the viral RNA genome (PubMed:18078692). During transcription, synthesizes subgenomic RNAs and assures their capping by a cap-snatching mechanism, which involves the endonuclease activity cleaving the host capped pre-mRNAs (By similarity). These short capped RNAs are then used as primers for viral transcription (By similarity). The deubiquitinating and deISGylating activities specifically cleaves poly-ubiquitinated conjugates and ISG15 from RIG-I, interfering with antiviral signaling pathways mediated by NF-kappaB and IRF signalings (PubMed:18078692, PubMed:21266548, PubMed:28877473). Deubiquitinates mono-ubiquitinated, K48- and K63-linked tetra-ubiquitinated molecules (PubMed:21228232). Favors K63 poly-Ub linkage (PubMed:23345508). Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Interacts (via N-terminus) with host ISG15 (via C-terminus); the deISGylase activity of the viral protein interferes with antiviral signaling pathways mediated by NF-kappaB and IRF signalings (PubMed:21266548, PubMed:21245344). Interacts with host ubiquitin (PubMed:21245344). The viral OTU domain (vOTU) and its N-terminal extension is responsible for ubiquitin and ISG15 binding and for the deubiquitination and deISGylation activities. Classified as His(+) endonuclease since it has a histidine upstream of the active site that coordinates the first cation. Belongs to the Bunyavirales RNA polymerase family.