FIG. 1.

CAT expression levels supported by different PB2 genes measured in a cell-based replication assay. Vero cells were transfected using DOTAP with plasmids directing expression of the PB2 gene along with either pGT-h-NP, derived from A/PR8/34, and pGT-h-PA or pGT-h-PB1, derived from A/WSN/33 (8) (a), or pHMG-FPV-NP, pHMG-FPV-PA, or pHMG-FPV-PB1, derived from A/FPV/Rostock/34 (23) (b), and pPolI-CAT-RT (26). At 48 h posttransfection, cell extracts were prepared and tested for CAT levels using previously described methods (25) (a) or a CAT ELISA kit (b).