Plays critical roles in regulating RNA replication and transcription through its interactions with multiple proteins (By similarity). Tethers the RNA-directed RNA polymerase L to the nucleoprotein-RNA complex (By similarity). Recruits the M2-1 protein, a processivity factor that is required for efficient transcription of viral RNA. Acts as a chaperone for neo-synthesized nucleoprotein by forming an N-P complex that preserves N in a monomeric and RNA-free state and prevents the association of nascent N with host cell RNAs. Recruits the host phosphatase PP1 to inclusion bodies to regulate viral transcription (By similarity). Homotetramer (By similarity). Interacts with protein M2-1; the interaction between the two tetramers is required for the anti-termination and elongation transcriptional activities of protein M2-1. Interacts with host phosphatase PP1; this interaction recruits PP1 to the inclusion bodies. Formation of a complex PP1/M2-1/P allows P to target host PP1 phosphatase to the M2-1 substrate. Interacts with the nucleoprotein N; the phosphorylated phosphoprotein P binds to N-RNA complex. Interacts with the monomeric RNA-free nucleoprotein N (By similarity). Interacts with RNA-directed RNA polymerase L (via N-terminus); the association of P and L forms the polymerase complex (By similarity). Localizes in cytoplasmic inclusion bodies. Constitutively phosphorylated by host. Belongs to the pneumoviridae phosphoprotein P family.