Nuclear Pores: David and Goliath in nuclear transport

Ran is the only known member of the Ras superfamily of small GTP-binding proteins to be localized primarily inside the nucleus, and there is considerable evidence that Ran is closely involved in the traffic of macromolecules into and out of the nucleus [1,2]. Ran has been shown to be an essential factor for nuclear import in digitonin-permeabilized cells, and mutant forms of Ran inhibit both protein import into the nucleus and mRNA export from the nucleus in vivo. Additional evidence of a role for Ran in nuclear transport has recently come from the discovery of a new nuclear pore complex protein, Nup358, that binds Ran directly.