1. European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany

Correspondence to: Iain W. MattajMartin Hetzer Email: mattaj@embl-heidelberg.de
Email: hetzer@embl-heidelberg.de

Abstract

In metazoa, the nuclear envelope breaks down and reforms during each cell cycle. Nuclear pore complexes (NPCs), which serve as channels for transport between the nucleus and cytoplasm¹, assemble into the reforming nuclear envelope in a sequential process involving association of a subset of NPC proteins, nucleoporins, with chromatin followed by the formation of a closed nuclear envelope fenestrated by NPCs^{2, 3, 4, 5, 6, 7}. How chromatin recruitment of nucleoporins and NPC assembly are regulated is unknown. Here we demonstrate that RanGTP production is required to dissociate nucleoporins Nup107, Nup153 and Nup358 from Importin , to target them to chromatin and to induce association between separate NPC subcomplexes. Additionally, either an excess of RanGTP or removal of Importin induces formation of NPC-containing membrane structures—annulate lamellae—both in vitro in the absence of chromatin and in vivo. Annulate lamellae formation is strongly and specifically inhibited by an excess of Importin . The data demonstrate that RanGTP triggers distinct steps of NPC assembly, and suggest a mechanism for the spatial restriction of NPC assembly to the surface of chromatin.