Crossing the Nuclear Pore Complex
'How proteins cross the Nuclear Pore Complex', a post from one of my favorite blogs, states the following in the first paragraph:
"Over this past summer I saw Dirk Görlich give a talk about how the multitude of FG repeats found within the nuclear pore complex (NPC), form a gel like matrix. This "elastic hydrogel" acts as the major barrier within the NPC. Although the gel can prevent the passage of most large molecules (>30kD), it is permeable to nuclear transport receptors (NTRs). Note that all this "story" was published in the November 3rd edition of Science Magazine (link). In that paper there's a nice diagram in the that explains it all:"
FG repeats are nucleoporin repeats that are rich in the amino acids phenylalanine and glycine. The many good diagrams are a staple of the referenced blog.