 The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes . Although small molecules can enter the nucleus without regulation , macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit . " <unk> " proteins that must be <unk> from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals , which are bound by importins , while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins . The ability of importins and exportins to transport their cargo is regulated by <unk> , enzymes that <unk> the molecule <unk> <unk> to release energy . The key <unk> in nuclear transport is <unk> , which can bind either <unk> or GDP ( <unk> <unk> ) , depending on whether it is located in the nucleus or the cytoplasm . Whereas importins depend on RanGTP to <unk> from their cargo , exportins require RanGTP in order to bind to their cargo . 
