Chromatin docking and exchange activity enhancement of RCC1 by histones H2A and H2B

The Ran guanosine triphosphatase (GTPase) controls nucleocytoplasmic transp ort, mitotic spindle formation, and nuclear envelope assembly. These functi ons rely on the association of the Ran-specific exchange factor, RCC1 (regu lator of chromosome condensation 1), with chromatin. We find that RCC1 bind s directly to mononucleosomes and to histones H2A and H2B. RCC1 utilizes th ese histones to bind Xenopus sperm chromatin, and the binding of RCC1 to nu cleosomes or histones stimulates the catalytic activity-of RCC1, We propose that the docking of RCC1 to H2A/H2B establishes the polarity of the Ran-CT P gradient that drives nuclear envelope assembly, nuclear transport, and ot her nuclear events.