The small GTPase Ran enzyme regulates critical eukaryotic cellular functions including nuclear transport and mitosis through the creation of a RanGTP gradient around the chromosomes. This concentration gradient is created by the chromatin bound RCC1 (regulator of chromosome condensation) protein which recruits Ran to nucleosomes and activates Ran’s nucleotide exchange activity. While RCC1 has been shown to bind directly with the nucleosome, the molecular details of this interaction were not known. We have determined the crystal structure of the RCC1-nucleosome core particle complex at 2.9 Å resolution, providing the first atomic view of how a chromatin protein interacts with the histone and DNA components of the nucleosome. Our structure also suggests that the Widom 601 DNA positioning sequence present in our nucleosomes forms a 145 bp and not the expected canonical 147 bp nucleosome core particle.
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