Nucleocytoplasmic transport is mediated by large supramolecular structures that span the nuclear envelope called nuclear pore complexes (NPC).

Classical import pathway involves proteins containing nuclear localization signal (NLS). This transport signal is recognized in the cytosol by importin α. Binding of the resulting complex to the cytoplasmic fibrils of the NPC is mediated by the cytosolic factor importin β. From there the substrate-α-β transport complex move to a central NPC region, where it pass through a gated channel [1,2]. This import as well as the export pathway are dependent on the GTPase cycle of Ran protein, a Ras-related GTPase.

Importin β proteins contain a conserved region in their N terminal part that is important for the binding of the Ran protein [3].

The eukaryotic proteins that contain such a domain are listed below:

• Importin-β 1 to importin-β 3 (also known as karyopherins β).
• Exportin, the receptor for the leucine-rich nuclear export signal (NES).
• Importin-α re-exporter. Mediates importin-α reexport from the nucleus to the cytoplasm after import substrates have been released into the nucleoplasm.
• Vertebrate RanBP7 protein and yeast homologue nonsense-mediated mRNA decay protein 5 (NMD5) of unknown function.
• Mammalian RanBP16 protein. It may function as a nuclear transport receptor.

The profile we developed covers the whole conserved region.