FRANCIS LEROY & OLIVIER WAUTIER, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY & OLIVIER WAUTIER, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Nuclear protein import, animation. The movement of small molecules such as proteins into the nucleus (bottom left) is regulated by nuclear pore complexes (top left) in the nuclear membrane. Proteins that are to be transported to the nucleus are tagged with nuclear localisation signals (NLS). Proteins called importins (dark blue) bind to this tag to facilitate the protein's movement through a nuclear pore (light blue). Once inside the nucleus the protein/importin complex is bound by ran-GTP (guanosine triphosphate), resulting in a conformational change in the importin that causes the release of the protein. The importin/ran-GTP complex travels back through the pore to the cytoplasm where the two components are separated. This allows the hydrolysis of GTP to GDP (guanosine diphosphate) and inorganic phosphate (Pi).
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