In mammalian cells, it is SUMO modified and attached to the cytoplasmic side of the nuclear pore complex via interaction with the nucleoporin RANBP2 (Nup358).

Cytoplasmic RanGDP is imported into the nucleus by the small protein NUTF2 (Nuclear Transport Factor 2), where RCC1 can then catalyze exchange of GDP for GTP on Ran.

Ran is involved in the transport of proteins across the nuclear envelope by interacting with karyopherins and changing their ability to bind or release cargo molecules.

During mitosis, the Ran cycle is involved in mitotic spindle assembly and nuclear envelope reassembly after the chromosomes have been separated.

In telophase, RanGTP hydrolysis and nucleotide exchange are required for vesicle fusion at the reforming nuclear envelopes of the daughter nuclei.

Polyglutamine repeat expansion in the AR is linked to spinal and bulbar muscular atrophy (Kennedy's disease).