Fig. 3.

Schematic representation identifying the main biochemical constituents of the nuclear import machinery. Passage through the NPC is restricted to transport receptors, which bind and chaperone NLS-cargo through the NPC, while access is prohibited for passive (non-NLS) molecules of similar size. Binding of RanGTP to the transport receptor releases the NLS-cargo into the nucleus. The gray shaded area emphasizes the location of the FG-domains and the question mark highlights the uncertainty with regard to the biophysical aspects of the selective gating mechanism within the NPC, which operates to restrict or promote cargo translocation