Figure 7.

VSVG and ssHRP are excluded from Golgi vesicles during transit through the Golgi complex. Human fibroblasts (a–c) and COS-7 cells (d–f) were subjected to the ER accumulation–chase protocol (D) or the large (C) or the intermediate (A and B) pulse protocols, fixed 7 min after the release of the temperature block (A–D), and then processed for labeling. In the experiments in (A) and (B) they were labeled for VSVG by the cryo-immunogold technique, in C by the nanogold gold enhance technique, and in D (which shows a tangential thick section), by the preembedding immunoperoxidase method. Also in A, the GM130 protein is labeled (small particles). (e and f) For ssHRP experiments, COS-7 cells were transfected with ssHRP, fixed at steady state, and then processed for detection of HRP. (E) Perpendicular and (F) tangential section. Irrespective of the labeling and sectioning technique, the round (vesicular) profiles (arrows) are almost always devoid of cargo, whereas cisternae are labeled. Bar: (A, D, and E) 110 nm; (B) 120 nm; (C) 90 nm; (F) 200 nm.