Fig. 2. Surfaces (A) and cross-sections (B) from the 3D reconstruction of mtMCM. The surface at the top is oriented so that the 7-fold axis is vertical, and the axial position of the sections (B) at –40, 0 and 40 Å are indicated. A very small detached density was present in the central channel, but was removed since simulations showed that it was consistent with noise. The heptamer is ∼100 Å in length along the 7-fold axis. The surface in the center corresponds to a ‘top’ view (showing the helicase domain, Figure 4).