Fig. 1. Concentration of VSVG in large, pleiomorphic structures upon release from the ER. Transmission electron micrographs of VSV-infected NRK cells subjected to the rapid ethane-freezing procedure 10 minutes after release from 40°C. (A) Low magnification micrograph (top panel) illustrating the presence of large, pleiomorphic structures (^*) with extensive bud profiles enriched with VSVG immunogold labeling (9 nm gold particles). Bar, 0.5 µm. The boxed region is magnified (bottom panel) to illustrate a single structure and its various features, including bud-profiles (BP) and the matrix (M). (B,C) These structures (^*) are segregated from COPII-labeled (Sec13 antibody, 9 nm gold particles) ER exit sites (Hong, 1998) (arrowheads). Bar, 0.2 µm. (D) These structures (^*) are devoid of markers of the Golgi stack (G), such as GS28 (Subramaniam et al., 1996), 9 nm gold particles (arrowheads). (E) Some of these structures (^*) can be found in the vicinity of the Golgi stack seemingly in the process of aligning and tethering with the Golgi stack for presumably a fusion event (G). Bar, 0.2 µm. (F) The structure (^*) shown here is in the process of fusing with a Golgi stack (G) and appears to be emptying its VSVG (9 nm gold particles) content into it. Bar, 0.2 µm.

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