Figure 2.

Single-virus fusion observed via fluorescence dequenching. (a) Example fluorescence micrographs of individual Zika virions (colored spots) bound to target vesicles (not visualized). At t = 0 (top) the virions’ fluorescence is self-quenched but detectable as a dim spot. After low pH buffer exchange, 2 of 3 particles in the field of view exhibit dequenching due to lipid mixing after 100 s (bottom). (b) The fluorescence intensity trace of the virion boxed in A shows a sudden jump to higher fluorescence due to lipid mixing followed by photobleaching. The hemifusion wait time is defined as the time between pH drop and the onset of lipid mixing.