Chromatin-independent nuclear envelope assembly induced by Ran GTPase in Xenopus egg extracts

The nuclear envelope (NE) forms a controlled boundary between the cytoplasm and the nucleus of eukaryotic cells. To facilitate investigation of mechan isms controlling NE assembly, we developed a cell-free system made from Xen opus laevis eggs to study the process in the absence of chromatin. NEs inco rporating nuclear pores were assembled around beads coated with the guanosi ne triphosphatase Ran, forming pseudo-nuclei that actively imported nuclear proteins. NE assembly required the cycling of guanine nucleotides on Ran a nd was promoted by RCC1, a nucleotide exchange factor recruited to beads by Ran-guanosine diphosphate (Ran-GDP). Thus, concentration of Ran-GDP follow ed by generation of Ran-GTP is sufficient to induce NE assembly.