Importins and exportins are group of proteins called karyopherins which are responsible for transporting molecules and other proteins from the cytoplasm to the cell nucleus. The process is normally facilitated via ingress and egress via nuclear pores which are distributed around the nuclear envelope.
Powered by the energy releasing Ran gradient, Importins bind to their molecular load, pass through the nuclear pore complexes and integrate with Ran-GTP to drop there load.
Exportins essentially reverse the process, within the nucleus the exportin binds to its cargo and exits via the nuclear pore complex to disassociate when the cargo movement is complete.