Mediates the import of GDP-bound RAN from the cytoplasm into the nucleus which is essential for the function of RAN in cargo receptor-mediated nucleocytoplasmic transport. Thereby, plays indirectly a more general role in cargo receptor-mediated nucleocytoplasmic transport. Interacts with GDP-bound RAN in the cytosol, recruits it to the nuclear pore complex via its interaction with nucleoporins and promotes its nuclear import. Homodimer (PubMed:7744965). Interacts with RAN (GDP-bound form); the interaction is direct and regulates RAN nuclear import (PubMed:10679025). Interacts with the nucleoporins NUP54, NUP58 and NUP62 (via FG repeats); recruits NUTF2 to the nuclear pore complex a step required for NUTF2-mediated GDP-bound RAN nuclear import (PubMed:7744965). Interacts with CAPG; mediates its nuclear import (PubMed:18266911). At steady state it is essentially nucleoplasmic, enriched in nucleoplasmic foci.