Quantification of cell-cell fusion in BHK cells cotransfected with expression plasmids encoding wt gB, gD, gH, and gL (40 ng of each) (A) or gBΔ867, gD, gH, and gL (20 ng of each) (B) plus pUL20-pcDNA and/or pgK (160 ng of each) and the pcDNA 3.1(−) Myc-His/Lac vector (80 ng). BDHL, gB, gD, gH, and gL. The amounts of DNA in the transfection mixtures were made equal by addition of pMTS1, as appropriate. Syncytium staining and quantification were performed as described in the legend to Fig. 2. The bars indicate SE.