Fig. 4. The sizes of ERES-like clusters in the simulation. The mean size <n> of ERES-like clusters decreases upon accelerating the binding kinetics (e.g. by depleting transport-competent cargo) in the case of biased binding (A) and free binding (B). Here, K_on was increased while keeping K_off=K_on/2, K_on, 2K_on (light grey, dark grey, black fill). Using biased binding – that is, a cooperativity of COPII complexes – the ERES-like clusters were significantly larger (compare B with A). (C) The distribution of normalized sizes, p(a) with a=n/<n> always showed a broad shape with a cut-off that is imposed by the smallest visible cluster.