BSR-T7 cells were plated in 96-well plates at 2 × 104 cells per well and transfected the day after with 66 ng of pEMC-N, 44 ng of pEMC-(Flag/L), 28 ng of pEMC-P construct (encoding either wt P or the individual P variants), and 90 ng of plasmid encoding for the minigenome, using jetPRIME (Polyplus). Two days after transfection, the firefly luciferase activity was measured using the Nano-Glo Dual-Luciferase Reporter Assay (Promega). The background luciferase activity observed in the absence of active L protein was subtracted from the signal measured in the presence of L, and data obtained from three independent experiments were normalized to each other using the mean signal observed for all combinations tested at the same time (12).