FIG. 4.

Fusion activity of I463A, I463F, and N211A mutants in the presence or absence of HN protein expression. Effector HeLa cells were cotransfected with mutant F- and HA-expressing pCAGGS as detailed in Materials and Methods. RBCs labeled with both R18 (red) and calcein (green) were then added. (A) Representative fields of HeLa cells coexpressing influenza virus HA and F mutants 210 min after being overlaid with R18/calcein-labeled RBCs. High levels of hemadsorption due to HA can be seen on the wild-type F-R18 field without probe transfer. (B) Time dependence of dye transfer (R18) in the presence or absence of HN. Data are means for triplicate experiments.