RNA-dependent RNA polymerase which is responsible for replication and transcription of virus segments. Binds the promoter sequence of the encapsidated viral RNA. Displays an endonuclease activity involved in cap-stealing. Cleaves cellular pre-mRNA to generate primers for viral transcription (By similarity). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) The RNA polymerase is composed of three subunits: PB1, PB2 and PA.