Non catalytic polymerase cofactor and regulatory protein that plays a role in viral transcription and replication. Stabilizes the RNA polymerase L to the N-RNA template and binds the soluble protein N, preventing it from encapsidating non-genomic RNA. Also inhibits host IFN-alpha and IFN-beta signaling by binding and retaining phosphorylated STAT1 in the cytoplasm or by inhibiting the DNA binding of STAT1 in the nucleus (By similarity). Homotrimer when phosphorylated. This trimer is stabilized by binding to the L protein. Binds soluble protein N, and ribonucleocapsid. Interacts with host STAT1, STAT2 and PML (By similarity). Phosphorylated by host PKC and by an unknown kinase. Belongs to the lyssavirus protein P family.