Fig. 5.

Double-membrane vesicles and the assembly of virus particles. (a) Double-membrane vesicles in cytopthic cells of intestine, typically composed of accumulations of multiple single-membrane (arrow) vesicles enclosed within an outer membrane (arrowhead). Bar, 100 nm. (b) Double-membranes vesicles (arrowhead), probably coming from rough endoplasmic reticula, and a double-membrane vesicle with a large space between the inner (arrow) and outer (open arrow) membranes of the vesicle, virus particles located between the membranes. Bar, 200 nm. (c) Some vesicles with dark blurry edge areas around clear membrane (arrow) are also found in the cytopathic cells. Bar, 200 nm. (d) The virions (arrowheads) always exist in the dark blurry margins around the membrane, if the vesicles are not full of virions; virions acquired an envelope by budding into the cisternae (arrows) and formed mostly spherical, sometimes pleomorphic, particles, which suggest these vesicles seem to be the site of the viral assembly. Bar, 200 nm.