Abstract
Exchange between the nucleus and the cytoplasm occurs through nuclear pore complexes (NPCs) embedded in the double membrane of the nuclear envelope. NPC permeability barrier restricts the entry of inert molecules larger than 5 nm in diameter but allows facilitated entry of selected cargos, whose size can reach up to 39 nm. The translocation of large molecules is facilitated by nuclear transport receptors (NTRs) that have affinity to proteins of NPC permeability barrier. Viruses that enter the nucleus replicate evolved strategies to overcome this barrier. In this review, we will discuss the functional principles of NPC barrier and nuclear transport machinery, as well as the various strategies viruses use to cross the selective barrier of NPCs.
Highlights
The double membrane of the nuclear envelope surrounds the nucleus and separates the cellular genome from the cytosol during interphase
The majority of facilitated translocations are mediated by nuclear transport receptors (NTRs) of the importin-β superfamily
The permeability barrier of the pore plays a dual role: it restricts the diffusion of inert molecules, whose mass exceed 20–40 kDa, but allows the passage of large NTR·cargo complexes, whose mass can reach several megadaltons
Summary
The double membrane of the nuclear envelope surrounds the nucleus and separates the cellular genome from the cytosol during interphase. NPCs are very large macromolecular assemblies with an approximate mass of 125 MDa in higher eukaryotes [6,7] This exceeds 25 times the mass of a eukaryotic ribosome [8], which points to the complexity of its biogenesis. The vertebrate NPC has an eight-fold rotational symmetry and contains multiple structural domains [9,10]. These include cytoplasmic filaments, nuclear and cytoplasmic rings, a scaffold of eight large spikes, a nuclear “basket” and, located in the central channel, the permeability barrier controlling the selectivity and the rate of nucleocytoplasmic exchange (Figure 1A)
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