Nucleoporin  Nucleoporins are a family of proteins which are the constituent building blocks of the nuclear pore complex (NPC). The nuclear pore complex is a massive structure embedded in the nuclear envelope at sites where the inner and outer nuclear membranes fuse, forming a gateway that regulates the flow of macromolecules between the cell nucleus and the cytoplasm. Nuclear pores enable the passive and facilitated transport of molecules across the nuclear envelope. Nucleoporins, a family of around 30 proteins, are the main components of the nuclear pore complex in eukaryotic cells. Nucleoporin 62 is the most abundant member of this family. Nucleoporins are able to transport molecules across the nuclear envelope at a very high rate. A single NPC is able to transport 60,000 protein molecules across the nuclear envelope every minute. Nucleoporins mediate transport of macromolecules between the cell nucleus and cytoplasm in eukaryotes. Certain members of the nucleoporin family form the structural scaffolding of the nuclear pore complex. However, nucleoporins primarily function by interacting with transport molecules known as karyopherins, also known as Kaps These karyopherins interact with nucleoporins that contain repeating sequences of the amino acids phenylalanine (F) and glycine (G) FG peptide repeats. In doing so, karyopherins are able to shuttle their cargo across the nuclear envelope. Nucleoporins are only required for the transport of large hydrophilic molecules above 40 kDa, as smaller molecules pass through nuclear pores via passive diffusion. Nucleoporins play an important role in the transport of mRNA from the nucleus to the cytoplasm after transcription. Depending on their function, certain nucleoporins are localized to either the cytosolic or nucleoplasmic side of the nuclear pore complex. Other nucleoporins may be found on both sides. It has been recently shown that FG nucleoporins have specific evolutionary conserved features encoded in their sequences that provide insight into how they regulate the transport of molecules through the nuclear pore complex (NPC). Nucleoporins aggregate to form a nuclear pore complex, an octagonal ring that traverses the nuclear envelope. The ring consists of eight scaffold sub-complexes, with two structural layers of COPII-like coating sandwiching some proteins that line the pore. From the cytoplasm to the nucleoplasm, the three layers of the ring complex is named the cytoplasm, inner pore, and nucleoplasm rings respectively.