Fig 7.

Substantial external energy is required to trigger morbillivirus prefusion F trimers. (A to D) Vero cells were transfected with standard F- or variant-expressing plasmid DNA in the presence or absence of 3g. IF was performed, as described in the legend of Fig. 2B and E, with the pairs of conformation-sensitive anti-F MAbs. To determine the MAb-binding ability with the indicated F trimers, mean fluorescence intensities were recorded by flow cytometry. In some experiments, brief heat shocks (10 min at the indicated temperatures) were performed prior to IF. (E and F) Cell-cell fusion induction after cotransfection of Vero-SLAM (for CDV) or Vero (for MeV) cells with plasmid DNA encoding CDV or MeV F and H proteins in the presence of increasing concentrations of the fusion inhibitor 3g. At 24 h posttransfection, cells were incubated at 42°C for 5 h (for CDV) or 8 h (for MeV) in the presence of 3g. Representative fields of view were captured at 24 h posttransfection with a fluorescence confocal microscope (Fluoroview FV1000; Olympus).