FIG. 5.

Limited but significant IBV fusion occurs at lower temperature. R18-labeled IBV strain Beaudette was bound to BHK cells at 4°C for 60 min and then added to a spectrofluorimeter cuvette at either 20°C or 37°C (t = 0 s). The pH was reduced to 5.0 at t = 100 s or maintained at 7.0 while FdQ activity was monitored.