Fig. 4.

Ultrastructural analysis of the putative SARS-CoV replication sites. (a, b) Vero cells were mock-infected (a) or infected with SARS-CoV (MOI of 10) for 3 h (b), fixed and analyzed by standard EM. Double membrane vesicles characteristic for SARS-CoV replication sites are highlighted with arrows. (c–e) Vero cells were infected with SARS-CoV (MOI of 10) for 3 h, fixed and analyzed by cryo-iEM. Cells were labeled with antibodies directed against SARS-CoV N (15 nm gold, filled arrowheads) and SARS-CoV nsp3 (5 nm gold, open arrowheads). Areas of colocalization of N and nsp3 are shown in panels c and d. Membrane tubules specific for these sites are marked with arrows. Sites where viral particles (marked with stars) were present only contained N labeling but almost no nsp3 labeling (e). Scale bars represent 200 or 500 nm as indicated.