Implicated in endonuclease cleavage of capped RNA primers. Displays an elongation factor activity in viral RNA synthesis. Dispensable for viral transcription, but not replication. Influenza RNA polymerase is composed of three subunits: PB1, PB2 and PA. Phosphorylated on serines and threonines by host kinases, including human casein kinase II. Belongs to the influenza viruses PA family.