Luciferase reporter gene assay HEK-293T, Hela or Vero cells were plated in 24-well plates (2610 5 cells per well). One day later, cells were transfected with either pISRE-Luc (0.3 mg/well; Stratagene) or pFA2-Elk1 (0.3 mg/well; Stratagene) and pGal4-UAS-Luc plasmids (0.3 mg/ well; provided by Dr. Y. Jacob) together with pRL-CMV reference plasmid (0.03 mg/well; Promega). Cells were simultaneously cotransfected with 0.3 mg/well of pCI-neo-36FLAG, pCI-neo or pmCherryC1 expression vectors encoding viral proteins as specified. 24 h after transfection, cells were stimulated with IFNb (Biosource) at 1000 IU/ml or starved for 6 h then stimulated with EGF (Upstate) at 100 ng/ml. 24 h post transfection, cells were lysed, and both firefly and Renilla luciferase activities in the lysate were determined using the Dual-luciferase Reporter Assay System (Promega). Reporter activity was calculated as the ratio of firefly luciferase activity to reference Renilla luciferase activity, and normalized so that positive control activity equals 100. When indicated, cells were treated with U0126 (Promega) at 20 mM final concentration upon EGF stimulation. Subcellular localization of Cherry-tagged hPIV3-C FL , C 1-89 and C 24-well plates containing coverslips were seeded with HEK-293T cells (2610 5 cells per well). One day later, cells were transfected with pmCherryC1 expression vector alone or encoding hPIV3-C FL , hPIV3-C 1-89 or hPIV3-C 90-195 . 36 h after transfection, cells were incubated with PBS-PFA 4% for 20 min at RT, then treated with PBS-Triton 0.05% for 15 min at RT to permeabilize the cells. Finally, cells were incubated for 10 min at RT in a PBS-PFA 4% solution containing DAPI (49-6-Diamidino-2-phenylindole) at 10 mg/ml. Preparations were mounted using Fluoromount-G (Southernbiotech), and imaging performed using a SP5 confocal miscroscope (Leica).