Fusion activity of CHAV-G and VSV-G analyzed in a cell-cell fusion assay.

A) BSR cells were transfected with plasmids expressing the full-length G proteins and RABV P-GFP to facilitate the observation of syncytia. At 24 h post-transfection, the cells were incubated for 10 min with cell medium adjusted to the indicated pH, and then replaced by fresh medium at pH 7.4. The cells were kept at 37°C for 1 h before fixation. Nuclei were stained with DAPI. All images are representative examples from at least three independent experiments. The scale is the same for all micrographs. B) Percentage of fluorescent cells having formed a syncytia (containing more than 3 nuclei) as a function of pH for both VSV_IND-G and CHAV-G. C) Distribution of the size of syncytia as a function of pH for both VSV_IND-G and CHAV-G (at each pH, the examined field corresponded to about 400 transfected fluorescent cells at pH7).