are likely to play a role in generating the complex
curvature of the NE pores. Although the placement of the CNCs in the NPC coat did not directly
address the organization of the central transport channel (fig. S13), it accounted for ~16 MD
of the total mass of the NPC, bridged the resolution gap between low-resolution EM analyses
and high-resolution crystallographic studies, and
suggested the evolutionary conservation of its
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O. Dreesen, A. Patke, D. C. Rees, S. O. Shan, P. Stravropoulos,
and K. Thierbach for critical reading of the manuscript; K. Kato
and K. Kato for their contributions at the initial stages of this
project; L. N. Collins for technical support; D. King for mass
spectrometry analysis; E. Hurt and P. Loppnau for material;
S. Koide for providing the phage display library; S. Gräslund for
the pSFV4 vector; P. Afonine for advice regarding structure
refinement in PHENIX; and J. Kaiser and the scientific staff
of Stanford Synchrotron Radiation Laboratory (SSRL) Beamline
12-2 and the National Institute of General Medical Sciences and
National Cancer Institute Structural Biology Facility (GM/CA) at the
Fig. 4. Architecture of the NPC coat. (A) Thirty-two copies of the yeast
CNC, shown in cartoon representation with a representative subunit colored as
in Fig. 1, docked into the cryoelectron tomographic reconstruction of the intact
human NPC (3), shown as a gray surface. The outer and inner cytoplasmic and
nuclear CNC rings are highlighted in orange, cyan, pink, and blue, respectively.
(B) Cartoon representations of 16 yeast CNC copies from the cytoplasmic side
of the NPC coat. Schematics indicating the positions assigned to Nup84CTD
and Nup133, which were not crystallized, are shown. (C) Interface between the
inner and outer CNC rings. Two views of the yeast CNC and its mate from the
inner ring are shown. (D) Orientation of the Nup120 b propeller relative to
neighboring coat Nups and the membrane. Portions of two CNCs from the
cytoplasmic outer ring are shown in cartoon representation. Green and cyan
shading indicate the positioning of Nup84CTD and Nup133, respectively. The
cyan line represents the N-terminal unstructured segment of Nup133 that
binds to Nup120 (9). A schematic representation of the ring-forming Nup120-
Nup133 interaction is shown below.