Kinetic analysis of translocation through nuclear pore complexes

The mechanism of facilitated translocation through nuclear pore complexes ( NPCs) is only poorly understood. Here, we present a kinetic analysis of the process using various model substrates. We find that the translocation cap acity of NPCs is unexpectedly high, with a single NPC allowing a mass flow of nearly 100 MDa/s and rates in the order of 10(3) translocation events pe r second. Our data further indicate that high affinity interactions between the translocation substrate and NPC components are dispensable for translo cation, We propose a 'selective phase model' that could explain how NPCs fu nction as a permeability barrier for inert molecules and yet become selecti vely permeable for nuclear transport receptors and receptor-cargo complexes .