Figure 10. Secretory cargo traffic... | Rockefeller University Press

Figure 10.

$Figure 10. Secretory cargo traffic during yeast cisternal maturation. (A) Diagram illustrating the inferred behavior of the fluorescent secretory cargo in maturing yeast cisternae. Green and blue represent early and late resident Golgi proteins, respectively, and black dots represent fluorescent cargo molecules. Progressive maturation is depicted from left to right. The cargo molecules initially travel passively in the maturing cisternae. During the late stage of maturation, a fraction of the cargo molecules recycle in transport vesicles, which are generated with the aid of the AP-1 adaptor, to cisternae that are undergoing the early-to-late transition. (B) Qualitative prediction, according to the scheme in A, of the fluorescence signals from resident Golgi proteins and the secretory cargo in a maturing yeast Golgi cisterna. The cargo signal is constant during the early stage of maturation, then rises during the early-to-late transition, then declines during the late stage of maturation. Compare to the simpler scheme in Fig. S1. (C) Computer simulation of steady-state cargo levels in maturing Golgi cisternae according to the scheme in A. Details of the simulation procedure are given in Materials and methods. The horizontal axis indicates cisternae of varying maturity, from the newly formed cisterna 1 to the terminally mature cisterna 5. The vertical axis indicates the number of simulated cargo molecules in each cisterna. A cargo molecule in cisterna 4 or 5 could recycle to cisterna 3 with a specified probability. For the simulation shown, the probability of recycling from cisterna 4 was 0.10, and the probability of recycling from cisterna 5 was 0.35, where the increasing probability reflects the late recruitment of AP-1 to the Golgi. Those probability values were chosen for illustrative purposes because they produce a reasonable match to the experimental data, with ∼70% more cargo molecules in the transitioning cisterna 3 than in earlier cisternae.$

Secretory cargo traffic during yeast cisternal maturation. (A) Diagram illustrating the inferred behavior of the fluorescent secretory cargo in maturing yeast cisternae. Green and blue represent early and late resident Golgi proteins, respectively, and black dots represent fluorescent cargo molecules. Progressive maturation is depicted from left to right. The cargo molecules initially travel passively in the maturing cisternae. During the late stage of maturation, a fraction of the cargo molecules recycle in transport vesicles, which are generated with the aid of the AP-1 adaptor, to cisternae that are undergoing the early-to-late transition. (B) Qualitative prediction, according to the scheme in A, of the fluorescence signals from resident Golgi proteins and the secretory cargo in a maturing yeast Golgi cisterna. The cargo signal is constant during the early stage of maturation, then rises during the early-to-late transition, then declines during the late stage of maturation. Compare to the simpler scheme in Fig. S1. (C) Computer simulation of steady-state cargo levels in maturing Golgi cisternae according to the scheme in A. Details of the simulation procedure are given in Materials and methods. The horizontal axis indicates cisternae of varying maturity, from the newly formed cisterna 1 to the terminally mature cisterna 5. The vertical axis indicates the number of simulated cargo molecules in each cisterna. A cargo molecule in cisterna 4 or 5 could recycle to cisterna 3 with a specified probability. For the simulation shown, the probability of recycling from cisterna 4 was 0.10, and the probability of recycling from cisterna 5 was 0.35, where the increasing probability reflects the late recruitment of AP-1 to the Golgi. Those probability values were chosen for illustrative purposes because they produce a reasonable match to the experimental data, with ∼70% more cargo molecules in the transitioning cisterna 3 than in earlier cisternae.