CEMOVIS reveals the presence of molecular arrays at the OSER membranes. A-B. OSER membranes from HEK293 cells transfected with calnexin-YFP were imaged by CEMOVIS as described in the legend for Figure 2. Large globular proteins/protein complexes were found arrayed at the surface of the delimiting membrane (A) and in the cytosolic space between the OSER membranes (B; arrays are indicated by arrowheads). Scale bar is 100 nm. C. Regions of interest within an OSER stack, encompassing two membranes. Arrowhead indicates presence of large complexes, as in A and B; scale bar is 100 nm. D. The boxed areas were rotated to align the membranes vertically, their Fourier transforms were calculated. The Fourier transforms were inspected for presence of strong reflections that would be indicative of ordered arrangement of the densities within the micrograph; the reflection in D corresponds to striations with a period of 56 Å-1. The masked transforms were used to produce a filtered image, visualizing the ordered features (D, rightmost panel). E. Ordered densities are confined to the individual intermembrane regions of interest. The indicated regions of interest were processed as described under "Materials and methods". Of the three adjacent regions, only region "2" shows a reflection in the Fourier transform. Open arrow indicates the cutting direction; white lines in the boxed area indicate the orientation of the ordered density between the membranes within region "2".