FIG. 5.

EM analysis of SARS-CoV-infected Vero E6 cells (panels A, B, D, and E, 9 h p.i.; panel C, 6 h p.i.) cryofixed by high-speed plunge freezing in liquid ethane, a step followed by freeze substitution with 1% osmium tetroxide and 0.5% uranyl acetate in acetone and embedment in epoxy LX-112 resin. (A) Low-magnification overview of a region rich in virus-induced DMVs (arrows) and mitochondria (M). The interior of the virus-induced vesicles was strikingly different from that in the images presented in Fig. 4, and clear double membranes were now found to surround the structures. (B) Close-up of virions outside of the cell, with the spikes on the virion surface illustrating the general high quality of samples prepared using cryofixation. (C) Close-up of virus-induced DMVs, showing the double membrane of the structure and the high electron density of the interior compared to those shown in Fig. 4C. (D) Example of apparent continuity (arrow) between the outer membrane of a DMV and a mitochondrion (M), as was occasionally observed. (E) Example of a possible intermediate (arrow) in DMV formation, reminiscent of the previously proposed “protrusion and detachment” model (40). Bars, 250 nm (A, C, D, and E) and 100 nm (B).