Nuclear transport refers to the mechanisms by which molecules move across the nuclear membrane of a cell. The entry and exit of large molecules from the cell nucleus is tightly controlled by the nuclear pore complexes (NPCs). Although small molecules can enter the nucleus without regulation,[1] macromolecules such as RNA and proteins require association with transport factors known as nuclear transport receptors, like karyopherins called importins to enter the nucleus and exportins to exit.[2][3]
^Watson, JD; Baker TA; Bell SP; Gann A; Levine M; Losick R. (2004). "Ch9-10". Molecular Biology of the Gene (5th ed.). Peason Benjamin Cummings; CSHL Press. ISBN978-0-8053-9603-4.