MINIREVIEW Flexible Gates: Dynamic Topologies and Functions for FG

The nuclear envelope is a physical barrier between the nucleus and cytoplasm and, as such, separates the mechanisms of transcription from translation. This compartmentalization of eukaryotic cells allows spatial regulation of gene expression; however, it also necessitates a mechanism for transport between the nucleus and cytoplasm. Macromolecular trafficking of protein and RNA occurs exclusively through nuclear pore complexes (NPCs), specialized channels spanning the nuclear envelope. A novel family of NPC proteins, the FG-nucleoporins (FG-Nups), coordinates and potentially regulates NPC translocation. The extensive repeats of phenylalanine-glycine (FG) in each FG-Nup directly bind to shuttling transport receptors moving through the NPC. In addition, FG-Nups are essential components of the nuclear permeability barrier. In this review, we discuss the structural features, cellular functions, and evolution-ary conservation of the FG-Nups. Subcellular compartmentalization of eukaryotic cells into organelles imparts functional and spatial separation of essen-tial cellular processes. Interorganellar communication, how-ever, is required to coordinate activities within the cell. The movement of molecules between the cytoplasm and a give