Viral polymerase activity of A/HK/218847/06 (H1N1) and A/HK/218449/06 (H3N2) influenza viruses. Polymerase activity was assayed in a minigenome system using a viral UTR-driven luciferase reporter gene. The 293T cells were transfected with plasmids containing PB2, PB1, PA, and NP genes from either H1N1 (A) or H3N2 (B) plus a luciferase reporter plasmid. Plasmids that did not contain PB1 were used as negative controls (white bars). After 24 h, luciferase activity was assayed in cell extracts. Results presented represent the means ± SE from three independent transfections.