Figure 5.

Comparison of lipid and content mixing fusion activity of WT HA and the Ala and Ser mutants. COS7 cells were transfected with plasmids (pSM) encoding WT, Ala, and Ser mutant HAs, and treated with neuraminidase and trypsin (T) or chymotrypsin (C) as described in the legend to Figure 3. The cells were incubated with RBCs labeled with both R18 (red) and Calcein AM (green), incubated in pH 5.0 fusion buffer for 2 min at 37°C, reneutralized, and observed with a confocal microscope.