Fig. 4.

F plus TM promote cell fusion. Quantitative fusion assay on cells expressing combinations of F, G, TM, and TM mutants. Vero cells were transfected with combinations of F, G, TM, or TM mutants. At 24 h.p.t., the cells were incubated with or without trypsin (1 μg/mL) for 30 min. After 3 h of further incubations, the cells were overlaid with BSR cells, and a luciferase assay was performed. Data from four independent experiments were normalized, setting luciferase activity from expression of F and G and TM (plus trypsin) at 100%. The F and G and TM (no trypsin) luciferase activity was 73% of the values for plus trypsin. All other “no trypsin” values were normalized by resetting 73–100%. MCS, vector of expression plasmid; TM del, plasmid expressing TM∆HL; TM L-A, plasmid expressing TM HL L131A.