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 (PubMed:1944575, PubMed:17435751, PubMed:20668449, PubMed:22215983, PubMed:11336674). 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 (PubMed:12194828, PubMed:17435751, PubMed:22215983). 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 (PubMed:22215983). Involved in the regulation of onset of chromosome condensation in the S phase (PubMed:3678831). Binds both to the nucleosomes and double-stranded DNA (PubMed:17435751, PubMed:18762580). Interacts with RAN (PubMed:17435751, PubMed:18762580, PubMed:29040603, PubMed:11336674). Interacts (via N-terminus and RCC1 repeats) with KPNA4 (PubMed:29042532). Interacts with ARRB2; the interaction is detected in the nucleus upon OR1D2 stimulation (PubMed:16820410). Predominantly nuclear in interphase cells (PubMed:12194828). Binds to mitotic chromosomes (PubMed:12194828, PubMed:17435751, PubMed:20668449). N-terminal methylation by METTL11A/NTM1 is required for binding double-stranded DNA and stable chromatin association. Di- and trimethylation produce a permanent positive charge on the amino group, which facilitates electrostatic binding to the phosphate groups on DNA, while inhibiting histone-binding. Methylated tail helps retain RCC1 on chromosomes during nucleotide exchange on Ran. Patients with Raynaud disease produce antibodies that bind to RCC1.