Identification of two novel RanGTP-binding proteins belonging to the importin beta superfamily

Nucleo-cytoplasmic transport comprises a large number of distinct pathways, many of which are defined by members of the importin beta superfamily of n uclear transport receptors. These transport receptors all directly interact with RanGTP to modulate the compartment-specific binding of their transpor t substrates. To identify new members of the importin beta family, we used affinity chromatography on immobilized RanGTP and isolated Ran-binding prot ein (RanBP) 16 from HeLa cell extracts. RanBP16 and its close human homolog ue, RanBP17, are distant members of the importin beta family. Like the othe r members of the transport receptor superfamily, RanBP16 interacts with the nuclear pore complex and is able to enter the nucleus independent of energ y and additional nuclear transport receptors.