RCC1 (regulator of chromosome condensation) is a 45 kD nuclear protein containing RCC1 repeats.This widely expressed protein associates with chromosomes and acts as a guanine nucleotide exchange factor (GEF) protein for Ras-related GTPase Ran. RCC1 is thought to maintain the Ran GTP gradient required for nucleocytoplasmic transport and spindle assembly across the interphase nuclear envelope and on condensed mitotic chromosomes. RCC1 regulates cell cycle and also plays a role in nuclear pore transport. Defects in RCC1 results in abnormal chromosome segregation and genomic instability. RCC1 is transcriptionally activated by Myc through E-box elements. RCC1 binds to chromatin in a binary complex with Ran. The Poly6164 antibody recognizes the N-terminal region of the human and mouse RCC1 protein and has been shown to be useful for Western blotting.