FIG 4.

In vitro fusion assays. RK13 cells were cotransfected with expression plasmids for EGFP, wild-type gB (gB^Ka), or mutated gB^B4.1 and, optionally, gH^Ka or gH^32/98, gD^Ka, and gL^Ka. One day posttransfection the areas of green fluorescing syncytia were measured, and total fusion activity was determined by multiplication of the mean syncytium area with the number of syncytia in 10 randomly selected fields. Fusion activities obtained with the four wild-type glycoproteins were set as 100%. Shown are the mean relative values and standard deviations of three independent experiments.