Guanine-nucleotide releasing factor that promotes the exchange of Ran-bound GDP by GTP, and thereby plays an important role in RAN-mediated functions in nuclear import and mitosis. Contributes to the generation of high levels of chromosome-associated, GTP-bound RAN, which is important for mitotic spindle assembly and normal progress through mitosis. Via its role in maintaining high levels of GTP-bound RAN in the nucleus, contributes to the release of cargo proteins from importins after nuclear import (By similarity). Involved in the regulation of onset of chromosome condensation in the S phase (PubMed:2361953). Binds both to the nucleosomes and double-stranded DNA (By similarity). Predominantly nuclear in interphase cells. Binds to mitotic chromosomes.