Fig 1.

Polymerase activity supported by PB2 mutants. (A to C) 293T (A), NPTr (B), and DF-1 (C) cells were transfected with pCAGGS 5092 PB1, PA, NP, and WT or mutated PB2 as well as pCAGGS Renilla and a virus-like firefly luciferase minigenome-expressing plasmid. Luciferase production was measured 12 h posttransfection. Values were normalized to Renilla expression and to the activity of the WT polymerase. (D to F) The levels of viral mRNA, cRNA, and vRNA synthesized by different RNA polymerase PB2 mutants normalized to that of the WT polymerase in 293T (D), NPTr (E), and DF-1 (F) cells. Expression of 50-92 NP mRNA was used as an internal control. Results are from one experiment, undertaken in triplicate, representative of three independent experiments. The statistical significance of differences in polymerase activity or RNA synthesis from that of WT was assessed by a two-tailed, unpaired Student t test (*, P < 0.05; **, P < 0.01; ***, P < 0.001).