Fig. 8. `Kiss and run' fusion between early/late endosomes. To further characterize and quantitate the transient `kiss and run' interactions between endosomes, cells were pulse-chased with a mixture of 100 nm BSA-coated latex beads and 16 nm BSA-gold particles for the indicated times. Endosomes containing either a mixture of 100 nm (arrows) and 16 nm (arrowheads) particles, or only one of the tracers were quantified at the electron microscope. The results obtained indicate that, at the earliest time point observed (15 minutes of internalization), the majority of endosomes contained the mixture of particles in control and rab5(Q79L)-expressing cells. At 150 minutes after endocytosis, the two tracers were segregated in different endosomes in contol cells, while a large proportion of endosomes still contained both of them in rab5(Q79L)-expressing cells. Quantitative analysis of these results is presented in the bottom panel. Bar, 100 nm.