Figure 4.
Lipid mixing at the cell surface precedes the content release from endosomes. (A) The kinetics of JRFL (circles) and HXB2 (triangles) fusion with TZM-bl cells. Waiting times from the shift to 37°C to the point of lipid (red symbols) or content (green symbols) transfer were measured, rank ordered, and plotted as cumulative distributions of the fraction of fused viruses over time. (B) Comparative kinetics of partial fusion at the cell surface (red circles), endosomal fusion (green circles), and of sequential lipid and content transfer exhibited during the 2-step events (red and green triangles, respectively). The time intervals between sequential content (TC) and lipid (TL) transfer were ranked and plotted as cumulative distribution (crosses). (C) The kinetics of lipid and content mixing during fusion of infectious R9 HIV-1 viruses with TZM-bl cells.