RNA-dependent RNA polymerase which is responsible for replication and transcription of virus RNA segments. The transcription of viral mRNAs occurs by a unique mechanism called cap-snatching. 5' methylated caps of cellular mRNAs are cleaved after 10-13 nucleotides by PA. In turn, these short capped RNAs are used as primers by PB1 for transcription of viral mRNAs. During virus replication, PB1 initiates RNA synthesis and copy vRNA into complementary RNA (cRNA) which in turn serves as a template for the production of more vRNAs. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Influenza RNA polymerase is composed of three subunits: PB1, PB2 and PA. Interacts (via N-terminus) with PA (via C-terminus). Interacts (via C-terminus) with PB2 (via N-terminus); this interaction is essential for transcription initiation. Phosphorylated by host PRKCA. Belongs to the influenza viruses polymerase PB1 family.