English: EnvA-driven virus fusion with an endosome. A virion co-labeled with the membrane marker, DiD (red), and with the diffusible content marker, NC-eGFP (green), travels toward the cell nucleus (stained with Hoechst-33342, blue). The release of the viral content into the cytosol, which is marked by disappearance of the green signal, corresponds to the formation of a fusion pore between the viral and endosomal membranes. The time elapsed after raising the temperature to initiate endocytosis and fusion is shown in the upper right corner. For details, see the legend to Figure 4.