Figure 2. Inner ring structure and interactions between spokes.

(A) The inner ring and associated membrane protein densities (silver) within the micelle ring are shown. The inner ring has been segmented into an inner layer (green), an intermediate adaptin-like layer (dark pink), and the membrane-interacting layer (light blue).

(B) The highly fenestrated architecture of the inner ring with gaps (asterisks) and membrane-spanning regions are revealed in a cross-section that also shows the central channel. A single spoke is outlined (dashed rhomboid).

(C) A “half ring” view of the inner ring is viewed from the pore membrane; the local 2-fold axis for the center spoke is indicated with a black ellipse.

(D) Central cross-sections through the spoke with molecular models depicted as rods are viewed from the side and top to show the open architecture with gaps and voids (asterisks). A local 2-fold axis in the plane is indicated with an arrow and “2”.

(E) A molecular model for Nups within the spoke is shown as “cylinders and planks.” Three views from left to right: a front view from the central channel, a side view, and a view from the cytoplasm. All views have platform density (silver) and single rod-like connectors in blue and gold.

(F) Molecular model for three spokes in the inner ring.

(G) Two Nup170 molecules form a major contact between adjacent spokes and may interact with an Ndc1 dimer at the local 2-fold axis with their β-propellers (βs).

(H) Three inter-spoke contacts are shown: a contact between adjacent Nsp1 complexes and a pair of symmetry-related contacts between the Nup192 NTD and Nup188 CTD tail that are indicated with black arrows. One Nup188-Nup192 contact is outlined with a dashed oval. Nic96 and new connectors are shown in blue and gold ribbons.