Visualization of individual fusion events between VSV and liposomes at low pH, in amorphous ice. (A) At pH 7.5, viral particles and liposomes do not fuse. (B) At pH 6.0, G shows the characteristic post-fusion conformation and numerous fusion events are observed. (C) At pH 5.5, individual fusion events can be seen. Fusion proceeds from the base of the virus, and G forms helical arrays on the cylindrical part of the viral particle.