Fig. 5.

Cell–cell fusion is enhanced by proteolytic cleavage. Wild-type S glycoprotein and the furin-site-containing mutants HTVR, HTR and SSLR were expressed in COS-7 cells, and fusogenicity was determined as described in Fig. 2B (Nussbaum et al., 1994, York et al., 2004). The number of blue syncytia relative to that in the wild-type S glycoprotein control is shown from four independent experiments, and error bars represent one standard deviation. Transfection efficiencies within each experiment were comparable.