Conformational states of the nuclear pore complex induced by depletion of nuclear Ca2+ stores.

The nuclear pore complex (NPC) is essential for the transit of molecules between the cytoplasm and nucleoplasm of a cell and until recently was thought to allow intermediate-sized molecules (relative molecular mass of approximately 10,000) to diffuse freely across the nuclear envelope. However, the depletion of calcium from the nuclear envelope of Xenopus laevis oocytes was shown to regulate the passage of intermediate-sized molecules. Two distinct conformational states of the NPC were observed by field emission scanning electron microscopy and atomic force microscopy. A central plug occluded the NPC channel after nuclear calcium stores had been depleted and free diffusion of intermediate-sized molecules had been blocked. Thus, the NPC conformation appears to gate molecular movement across the nuclear envelope.