May regulate the intracellular trafficking of RAN (PubMed:11290418). Promotes guanine nucleotide release from RAN and inhibits binding of new GTP by preventing the binding of the RAN guanine nucleotide exchange factor RCC1 (PubMed:29040603). Regulates the levels of GTP-bound RAN in the nucleus, and thereby plays a role in the regulation of RAN-dependent mitotic spindle dynamics (PubMed:29040603). Enhances the expression of SCN5A at the cell membrane in cardiomyocytes (PubMed:18184654, PubMed:23420830, PubMed:21621375). Monomer. Interacts with RAN, both RAN-GTP and RAN-GDP (PubMed:11290418, PubMed:29040603). Competes with RCC1 for a common binding site on RAN and thereby inhibits RCC1-mediated nucleotide exchange (PubMed:29040603). Forms a complex with RAN-GTP and RANBP1 (By similarity). Interacts with the cytoplasmic loop 2 of SCN5A (PubMed:18184654). May shuttle between the nucleus and cytoplasm. Isoform 1 and isoform 2 are ubiquitously expressed (PubMed:11290418). Detected in heart and brain (PubMed:21621375). Overexpression can rescue the trafficking defect caused by some SCN5A mutations that impair trafficking to the cell membrane. Belongs to the MOG1 family.