FIGURE 5.

Disulfide bond reduction can restore fusion support function. A, visual assessment of syncytium formation. Vero cells were co-transfected with the indicated H, standard F, and GFP expression plasmids and incubated with FIP, a fusion inhibitor. Twenty-four hours post-transfection cells were washed and treated either with PBS (−DTT, top row of panels) or with 15 mm DTT (+DTT, bottom row of panels) for 30 min. Fusion score was recorded 3 h after DTT treatment. B, fusion scores. The extent of fusion before or after DTT treatment is indicated above each residue. Red empty box, fusion score of 0; one-third filled orange box, fusion score of 1; and two-thirds filled blue box, fusion score of 2. The central segment is indicated.