For quantification of virus morphology at different time points p.i., fixed cell culture supernatants were purified by centrifugation over a sucrose cushion, pelleted for 30 min at 40,000 g, 4uC in a Beckman ultracentrifuge using a TLA-55 rotor. Pellets were embedded in 12% gelatin and prepared for EM as described previously [50] . 70 nm cryosections were obtained with a Leica EM UC6 microtome, FC6 cryochamber (Leica Microsystems, Wetzlar, Germany) and a diamond knife (Diatome, DiS-Galetzka Weinheim, Germany). Thawed cryosections were counterstained with uranyl acetate as described elsewhere [51] . For EM and ET of infected cells, HUH-7 cells were grown on carbon-coated sapphire disks, infected and fixed as described above. Samples were high-pressure frozen with a BalTec HPM-010 and freeze substituted with 0.1% (w/v) uranyl acetate, 1% osmium tetroxide (w/v) and 5% (v/v) water in glass distilled acetone in a temperature-controlling device (Leica EM AFS I). Cells were kept for 40 h at 290uC and warmed up to 0uC (slope 5uC/h) with an additional 3 h infiltration period at 230uC. Samples were washed three times with glass distilled acetone, infiltrated at room temperature with increasing concentrations of epoxy resin (Glycidether 100, Roth, Karlsruhe, Germany) in acetone over 12 h, and polymerized at 60uC for 48 h. 150 nm and 300 nm sections were obtained with a Leica Ultracut UCT microtome and a diamond knife.