Nuclear poresare largeproteincomplexes that cross thenuclear envelope, which is the doublemembranesurrounding theeukaryoticcellnucleus. There are about an average of 2000 nuclear pore complexes (NPCs), in the nuclear envelope of a vertebrate cell, but it varies depending on cell type and the stage in the life cycle. The proteins that make up the nuclear pore complex are known as nucleoporins. About half of the nucleoporins typically contain either analpha solenoidor abeta-propellerfold, or in some cases both as separatestructural domains. Each NPC contains at least 456 individual protein molecules and is composed of 30 distinct proteins (nucleoporins).[1]The other half show structural characteristics typical of "natively unfolded" orintrinsically disordered proteins, i.e. they are highly flexible proteins that lack ordered secondary structure.[2]These disordered proteins are theFGnucleoporins, so called because their amino-acid sequence contains many repeats of the peptidephenylalanine—glycine.[3]
