The nuclear envelope in all eukaryotic cells is perforated by nuclear pores, that consist of the nuclear pore complex (NPC). The NPC is a highly complex supramolecular structure that plays a pivotal role in the trafficking of macromolecules and particles between the nucleus and the cytoplasm. During the past two decades a large body of information has accumulated on both the structure and role of the NPC. The diameter of NPC is about 120 nm and is composed of approximately 100 proteins.

The NPC structure has been elucidated using various electron microscopy techniques. The basic structure of the NPC is comprised of three concentric rings, each displaying an 8-fold symmetry. The cytoplasmic and nuclear rings are vertically integrated by eight spokes that approximately span the width of the nuclear envelope. A set of eight fibers extends from the nucleoplasmic ring into the nucleus, and are joined at the distal ends by a ring to form the so called basket.