Fig. 1. Architecture of outer COPII coat vertices.

a Slices through different z heights of a binned and filtered representative cryo-tomogram of wild-type COPII-coated tubule. In the top panel, density for the inner coat lattice is visible from the top and is indicated by a blue arrow, while the outer coat is cut through its side (red arrow). In the bottom panel, the outer coat is visible from the top, with its characteristic lozenge pattern (red arrow). Scale bar 50 nm. These images are representative of tubes seen on 286 tomograms from two separate experiments and data collection sessions. b Schematic representation of outer coat architecture. Sec13–31 subunits arrange in a lozenge pattern, around the inner coat that arranges in a tightly packed lattice. c, d Focus on the structure of vertices, boxed in this schematics. c Top and side views of the 12 Å subtomogram average of the COPII vertex, with rigid-body fitted models (PDB 2PM6 and 2PM9). Sec31 protomers in dark red and orange, Sec13 in grey. d Top panel: Domain organisation of wild-type Sec31, and the ΔNTD mutant. Middle panel: a sec31Δ yeast strain transformed with the indicated plasmids was tested on 5-FOA, revealing lethality associated with deletion of the NTD. Bottom panel: the same experiment repeated with a sec31Δ emp24Δ yeast strain reveals that depletion of emp24 rescues the lethality associated with deletion of the Sec31 NTD. Sigma threshold for contouring was set at 2.2 in (c, d). A representative result is shown from at least three replicates.