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 (PubMed:31698413). Recruits the M2-1 protein, a processivity factor that is required for efficient transcription of viral RNA (By similarity). 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 (By similarity). Recruits the host phosphatase PP1 to inclusion bodies to regulate viral transcription (By similarity). Homotetramer (PubMed:31698413). 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 (By similarity). Interacts with host phosphatase PP1; this interaction recruits PP1 to the inclusion bodies (By similarity). Formation of a complex PP1/M2-1/P allows P to target host PP1 phosphatase to the M2-1 substrate (By similarity). 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 (PubMed:31698413). Localizes in cytoplasmic inclusion bodies. Constitutively phosphorylated by host. Belongs to the pneumoviridae phosphoprotein P family.