The nucleus of eukaryotic cells is surrounded by a double membrane system, the nuclear envelope. The outer nuclear membrane is continuous with the endoplasmic reticulum. This compartmentalization generates a requirement for exchange of macromolecules between nucleus and cytoplasm, a process, which is mediated by nuclear pore complexes (NPCs). These macromolecular assemblies fuse the inner and outer nuclear membrane and form aqueous channels for translocation. NPCs facilitate unchallenged passive diffusion of small molecules and control the translocation of larger cargos in a highly selective manner.
We have studied the structure of NPCs in several species using cry-electron tomography. Subvolumes of the tomograms containing individual NPCs were extracted in silico and subjected to three-dimensional classification and averaging that results in an isotopically sampled structure. Beyond showing structure of NPCs, we identify major differences between higher and lower eukaryotes. Finally, insight into the organization of the NPC gate is resolved.