Stefan Petrovic1,3, George W. Mobbs1,3, Christopher J. Bley1,3, Si Nie1,3, Alina Patke2 and André Hoelz1 1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA 2Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, USA Correspondence: hoelzcaltech.edu

↵3 These authors contributed equally to this work.

The nucleus, a genome-containing organelle eponymous of eukaryotes, is enclosed by a double membrane continuous with the endoplasmic reticulum. The nuclear pore complex (NPC) is an ∼110-MDa, ∼1000-protein channel that selectively transports macromolecules across the nuclear envelope and thus plays a central role in the regulated flow of genetic information from transcription to translation. Its size, complexity, and flexibility have hindered determination of atomistic structures of intact NPCs. Recent studies have overcome these hurdles by combining biochemical reconstitution and docking of high-resolution structures of NPC subcomplexes into cryo-electron tomographic reconstructions with biochemical and physiological validation. Here, we provide an overview of the near-atomic composite structure of the human NPC, a milestone toward unlocking a molecular understanding of mRNA export, NPC-associated diseases, and viral host–pathogen interactions, serving as a paradigm for studying similarly large complexes.