The vertebrate nuclear pore complex (NPC) is a macromolecular assembly of 
protein subcomplexes forming a structure of eightfold radial symmetry. The NPC 
core consists of globular subunits sandwiched between two coaxial ring-like 
structures of which the ring facing the nuclear interior is capped by a fibrous 
structure called the nuclear basket. By postembedding immunoelectron microscopy, 
we have mapped the positions of several human NPC proteins relative to the NPC 
core and its associated basket, including Nup93, Nup96, Nup98, Nup107, Nup153, 
Nup205, and the coiled coil-dominated 267-kDa protein Tpr. To further assess 
their contributions to NPC and basket architecture, the genes encoding Nup93, 
Nup96, Nup107, and Nup205 were posttranscriptionally silenced by RNA 
interference (RNAi) in HeLa cells, complementing recent RNAi experiments on 
Nup153 and Tpr. We show that Nup96 and Nup107 are core elements of the NPC 
proper that are essential for NPC assembly and docking of Nup153 and Tpr to the 
NPC. Nup93 and Nup205 are other NPC core elements that are important for 
long-term maintenance of NPCs but initially dispensable for the anchoring of 
Nup153 and Tpr. Immunogold-labeling for Nup98 also results in preferential 
labeling of NPC core regions, whereas Nup153 is shown to bind via its 
amino-terminal domain to the nuclear coaxial ring linking the NPC core 
structures and Tpr. The position of Tpr in turn is shown to coincide with that 
of the nuclear basket, with different Tpr protein domains corresponding to 
distinct basket segments. We propose a model in which Tpr constitutes the 
central architectural element that forms the scaffold of the nuclear basket.