Figure 5.

A linear three-compartment model. The model comprises three different coats (A–C), each with an affinity for SNAREs (coat A for SNAREs X and U, coat B for SNAREs Y and V, and coat C for SNAREs P and Q), which mediate fusion by pairing (X with U, Y with V, and P with Q). The scheme illustrates the concentration of the three SNAREs in different compartments, which could represent the ER, the Golgi, and endosomes, and the net vesicle fluxes between them. The lengths of the arrows correspond approximately to the magnitude of the net fluxes with the three different coats. Note that each compartment attracts from the other compartments those vesicles that have budded with the coat that has a preference for the SNARE accumulating in it (e.g., compartment 2 attracts coat B vesicles and accumulates SNAREs Y and V). Three cargo proteins (cargos 1, 2, 3) with preferential affinities for coats A, B, and C, respectively, are concentrated in the different compartments. Calculated concentrations corresponding to the scheme are given in Supplement 5, Table, a.