Nuclear pore complexes (NPCs) are the exclusive gate of entry/exit of macromolecules into and out of the nucleus of living cells. They exhibit a unique selectivity in transport, with respect to size and molecular species: very small molecules can diffuse efficiently through the pore, while larger objects are delayed/blocked unless they are bound to specialized proteins, so called nuclear transport receptors (NTRs). The permeability barrier and its selectivity arise from an assembly of protein domains that are rich in phenylalanine-glycine repeats (FG repeat domains). These domains are natively unfolded and grafted at high density to the NPC channel walls. NTRs can interact with the FG repeat domains, thereby facilitating translocation of NTR-bound cargo.The supramolecular organization of the nuclear pore permeability barrier and the mechanism behind selective transport remain insufficiently understood. Our goal is to understand the relation between the organizational and dynamic features of FG-nucleoporin assemblies, their physicochemical properties, and the resulting biological functions. Using an approach that combines tailor-made biomimetic in vitro model systems, surface-sensitive in situ analysis techniques, and polymer physics theory, we will quantitatively study these relationships on the supramolecular level, a level that – for this type of assemblies – is hardly accessible with conventional biological and biophysical approaches. The model systems will be well-defined allowing tight control over composition and supramolecular structure. In a second step, we will apply the obtained knowledge and construct a biosynthetic in vitro system that performs active, directed macromolecular transport.If successful, this highly interdisciplinary project will greatly increase our mechanistic understanding of nuclear transport. It will also enable the development of novel biotechnology such as species-selective molecular separation devices.