Fig. 3. (A) 3D reconstruction of VP40(31–319). The threshold was set to visualize only the N-terminal domain (see Materials and methods). The 3D reconstruction is shown in the end view orientation (left) and side view orientations (middle and right). The right-most view is the middle view rotated by 60° along the 3-fold axis. The measurements of the particle are approximately as follows: outside diameter ∼90 Å; inside diameter ∼35 Å; height ∼25–30 Å; width of the dimer ∼55 Å. (B) 3D reconstruction of the VP40(31–212) ring structures (Ruigrok et al., 2000b). The reconstruction shown was calculated with a threshold corresponding to the volume of the N-terminal domain. The dimensions of the particle are similar to those shown in (A). (C) Model reprojections and class-averaged views used for the reconstruction calculations of VP40(31–319) (upper and middle panel, respect ively) and class-averaged views used to calculate the reconstruction of VP40(31–212) (lower panel; Ruigrok et al., 2000b). The reprojections and average views are shown from end views (left) to side views (right) every 10°. The arrows in the reprojections of VP40(31–319) reconstructions indicate extra density that is not visible in the VP40(31–212) images. These densities are also visible in the averaged images in the middle panel, but not in the class-averaged views of VP40(31–212) (lower panel) missing most of the C-terminal domain (Ruigrok et al., 2000b). (D) 3D reconstruction of VP40(31–319) with a threshold value that allows for visualization of the C-terminal domains represented by lower density. As a result of lowering the threshold, the N-terminal part has also increased in size.