  Nuclear pore complexes (NPCs) are very selective filters that monitor the
transport between the cytoplasm and the nucleoplasm. Two models have been
suggested for the plug of the NPC. They are (i) it is a reversible hydrogel or
(ii) it is a polymer brush. We propose a mesoscopic model for the transport of
a protein through the plug, that is general enough to cover both. The protein
stretches the plug and creates a local deformation. The bubble so created
(prtoein+deformation) executes random walk in the plug. We find that for faster
relaxation of the gel, the diffusion of the bubble is greater. Further, on
using parameters appropriate for the brush, we find that the diffusion
coefficient is much lower. Hence the gel model seems to be more likely
explanation for the workings of the plug.
