Structure-function relationship of the influenza virus RNA polymerase subunits

Influenza virus RNA polymerase with the subunit structure PB1-PB2-PA is involved in both transcription and replication of the RNA genome. PB1 is the catalytic subunit and binds both to PB2 in its N-terminus and to PA in its C-terminus. PB2 is required for priming with cap and binds to PB1 in its N-terminus. PA is required for cRNA-->vRNA synthesis of genome replication and binds to PB1 in its C-terminus. Therefore, PB1 is the core subunit not only for RNA polymerase activity but also complex formation of the enzyme. Protease activity is identified in the N-terminal region of PA, but its role on viral proliferation remains unknown.