FIG. 7.

Content mixing occurs following low-pH-induced IBV fusion at the cell surface. IBV strain Beaudette (multiplicity of infection, 5 infectious units/cell) was bound to the surfaces of BHK cells at 4°C for 60 min and was treated with 15 μM monensin to block virus entry from endosomes or was left untreated as a control. In the pH 5 pulse sample, the buffer pH was reduced to 5.0 in the presence of 15 μM of monensin for 2 min at 37°C and then replaced with 2% Dulbecco's modified Eagle's medium with monensin at 37°C for 8 h. Genome delivery and viral replication were monitored by expression of S glycoprotein via immunofluorescence microscopy. For quantification, >100 cells were scored in three independent experiments. The error bars represent the standard deviations of the mean.