Nuclear protein import.

The defining feature of eukaryotic organisms is the cell nucleus. All nuclear proteins are synthesized in the cytoplasm and need to be imported through the nuclear pore complexes (NPCs) into the nucleus. Import can be directed by various signals, of which the classical nuclear localization signal (NLS) and the M9 import signal are the best characterized. The past year has provided insight into the functions of the key players in NLS- and M9-dependent import, the interactions of these key players and possible implications of these interactions for the import mechanism. Although an understanding of some of the steps in the import process is emerging, the molecular mechanism of the actual translocation through the NPC is still obscure.