Control of influenza virus growth by cellular proteins

Influenza virus RNA polymerase is composed of three viral P proteins (PB1, PB2 and PA) and involved in both transcription and replication of the viral RNA genome. Using recombinant baculoviruses, we constructed the PA-PB1-PB2 (3P) complex and two kinds of 2P complex (PA-PB1 and PB1-PB2). The 3P complex is not fully active but vRNA acts as "RNA effector" for its conversion into an active form. The cap structure (⁷mGpppAm) also plays an allosteric effector for RNA polymerase activation. The PB1-PB2 complex carries the catalytic specificity of transcriptase, while the PA-PB1 complex harbors the replicase specificity. We propose that the 3P and PB1-PB2 complexes behave as the transcriptase whereas the PA-PB1 complex has the specificity of replicase. A host factor(s) seems to be involved in the functional conversion of 3P complex. The candidate host factors have been isolated using yeast two-hybrid screening