FIG. 7.

Serial-section analysis demonstrating a lack of continuity of the membrane forming the IV particles within the viral factories with any preexisting cellular membranes. HeLa cells were infected with VV strain WR, and at 16 h p.i. the cells were processed for serial-section analysis using conventional electron microscopy. Shown are 60-nm-thick serial sections through a virus factory. The arrowheads point to the first crescent-shaped convex membranes with spicules that form in the viral factory. Note that at these first stages of development there is no continuity between the forming ends and cellular membranes. Asterisks indicate larger spherical structures derived from the earlier crescents and which appear closed in some section planes (E and F) but are still forming in other section planes (C and D) with no continuity with any cellular membrane. Other profiles are of fully formed spherical IV particles (arrows). Bar, 200 nm.