Essential component of the RNA polymerase transcription and replication complex. Binds the viral ribonucleocapsid and positions the L polymerase on the template. May act as a chaperone for newly synthesized free N protein, so-called N(0). Plays a role in virion assembly. Homotrimer when phosphorylated in domain I. This trimer is stabilized by binding to the L protein (PubMed:2845648). Binds N(0), and N in ribonucleocapsid (PubMed:2845648). Sequences comparison studies have defined several domains. Domain I binds the protein L, contains phosphorylation sites required for trimerization and is involved in transcription. Hinge region is highly variable and may act as a spacer between domain I and II. Domain II is also phosphorylated, binds protein L, and plays a role in replication. Domain III is basic and essential for binding the N-RNA template. Domain I is phosphorylated by host CK2. Domain II is phosphorylated by other unknown kinases. Phosphorylation play an important role in facilitating trimerization and possibly P-L complex formation (By similarity). Belongs to the vesiculovirus protein P family.