Figure 2.

Freeze-fracture views of Golgi cisternae and transport vesicles. (A) Golgi area of a CHO cell in situ. Concave P-faces mostly have been exposed, revealing a relatively high particle density on cisternal and vesicle membranes at one pole and a relatively low particle density on cisternae and vesicles at the other pole. The particle-rich Golgi pole is the cis-pole; the particle-poor pole is the trans-pole. P-faces of a particle-rich endoplasmic reticulum cisternae (ER) and of a tortuous, particle-poor trans-Golgi network (TGN) can also be observed. (B) B–E are from isolated Golgi incubated to reconstitute transport in the presence of cytosol, ATP, and GTPγS (17). Particle-rich cisternal P-face (= cis-pole) showing an emerging particle-rich bud (facing arrows). A free vesicle and a budding vesicle (concave P-face) are observed in the vicinity of the cisternal membrane (arrows), each with a particle density comparable to that of the cisterna. (C) Particle-rich cisternal membrane (= cis-pole) with a particle-rich bud emerging (facing arrows) and two particle-rich free vesicles (arrows). All are exposed as concave P-faces. (D) Particle-poor cisternal P-face (= trans-pole) with two particle-poor buds in the process of emerging from the parental membrane (facing arrowheads). Two particle-poor vesicles (P-faces) are seen neighboring the cisterna (arrowheads). (E) Particle-poor cisternal P-face with a particle-poor bud (facing arrowheads) and three particle-poor vesicles, all exposed as P-faces. See Table 1 for the quantitation of the respective particle densities. (Magnifications: A–E, ×79,000; Bar = 100 nm.)