Fig. 6.

Putative intermediate structures in the formation of DMVs. The greyscale top images are virtual slices (6 nm thick) extracted from tomograms of EAV-infected HuH-7 cells. (A–C) Putative intermediates of an enwrapping process. The membranes of interest are highlighted in orange in the lower images. (A) Paired ER membranes, possibly corresponding to the stage sketched in Fig. 5A as II. This type of paired membranes could progressively curve (B) to form a vase-like double-membrane compartment (C, D) (stage represented in Fig. 5A as III) with an opening to the cytosol (white arrows). (D) 3D-surface rendering of the structure shown in panel C. (E–G) Structures compatible with intermediates in a double-budding mechanism. In the lower panels, the membranes are highlighted in dark blue (ER) and light blue (luminal vesicle). These structures could represent a stage between III and IV in Fig. 5B, in which a luminal vesicle interacts with an ER membrane that curves towards the cytosol, possibly to form the outer membrane of a nascent DMV. (G) 3D surface-rendered model of the structure shown in panel E. (H) Example of a DMV that is connected to the ER though it lacks the electron dense core usually seen in DMVs. The membranes are highlighted with purple (ER membranes) and pink (inner vesicle). Scale bars, 100 nm. See Supplementary information for experimental details. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)