Fig. 5. Ultrastructure of ER bud sites in Sec13-suppressed cells. Electron micrographs of high-pressure-frozen and freeze-substituted HeLa cells. (A) In control (lamin-A/C depleted) cells, small 50 nm vesicles are in close proximity to the Golgi apparatus (G). These vesicles are presumptive ER-to-Golgi transport vesicles but could potentially be either COPI- or COPII-coated. Occasionally, a coated (COPII) budding profile can be observed emanating from the ER (arrowhead). (B,C) In Sec13-depleted cells, the small 50 nm vesicles can still be observed (arrows) but, in addition, dilated ER with several budding profiles can frequently be seen (B, inset in C shows magnification of indicated area, large white arrowhead). These budding profiles (arrowheads in C) appear to be in different states of fission and contain an electron-dense coat. Scale bar: 500 nm (A,B), 350 nm (C).