FIG. 6.

F-mediated fusion is dependent on the HN concentration. (A and B) Vero cells were transfected with plasmids encoding luciferase (400 ng/well) and wt F or F-Yn (400 ng/well) and increasing amounts of plasmid encoding HN or Yc-HN. Cells were overlaid with BSR-T7 cells at 20 h posttransfection. After 7 h, the cells were lysed and the luciferase activity (expressed in RLU) was determined. The standard deviations of results for triplicate samples are shown. (C) Vero cells were transfected as described in the legend to panels A and B or infected with PIV5 at 3 PFU/cell for comparison. Cells were radiolabeled, surface proteins were biotinylated, and surface-expressed F or HN was immunoprecipitated (IP) and visualized by SDS-PAGE. For the anti-F IP, the amount of HN or Yc-HN DNA used in cotransfection was 1,500 ng/well.