Karyopherins are proteins involved in transporting molecules between the cytoplasm and the nucleus of a eukaryotic cell. The inside of the nucleus is called the karyoplasm (or nucleoplasm). Generally, karyopherin-mediated transport occurs through nuclear pores which act as a gateway into and out of the nucleus. Most proteins require karyopherins to traverse the nuclear pore.
Karyopherins can act as importins (i.e. helping proteins get into the nucleus) or exportins (i.e. helping proteins get out of the nucleus). They belong to the nuclear pore complex family[1] in the transporter classification database (TCDB). Energy for transport is derived from the Ran gradient.
Upon stress, several karyopherins stop shuttling between the nucleus and the cytoplasm and are sequestered in stress granules, cytoplasmic aggregates of ribonucleoprotein complexes.[2][3]