Nuclear Protein Transport: Key Concepts and Mechanisms

Protein targeting sequence

A sequence that directs a protein to its specific organelle.

Receptor

A protein that recognizes the protein targeting sequence.

Protein transport complex

A complex that binds to the receptor-cargo complex for transport.

Nucleus

An organelle surrounded by a double membrane, known as the nuclear envelope.

Nuclear envelope

The double membrane that surrounds the nucleus and contains nuclear pore complexes (NPCs).

Nuclear pore complexes (NPCs)

Structures that facilitate the transport of molecules such as proteins and mRNA across the nuclear envelope.

Macromolecules

Large molecules that are limited in their passage through the NPC.

FG-Nups

Central phenylalanine-glycine repeats that establish a barrier in the NPC.

Importins

Nuclear transport receptors that mediate the import of proteins into the nucleus.

Exportins

Nuclear transport receptors that mediate the export of proteins from the nucleus.

Nuclear localisation signal (NLS)

A sequence that directs proteins to the nucleus, consisting of basic amino acids.

Classical NLS (cNLS)

A type of NLS that consists of a stretch of basic amino acids, such as lysine and arginine.

Monopartin

A type of cNLS that consists of a single part, such as SV40.

Bipartin

A type of cNLS that consists of two parts, such as nucleoplasmin.

Ran-GTP cycle

A cycle involving the protein Ran that is required for nuclear trafficking.

GTP-bound Ran

The form of Ran that exists inside the nucleus.

GDP-bound Ran

The form of Ran that exists outside the nucleus.

Ran gradient

The difference in concentration of Ran-GTP and Ran-GDP that drives nuclear import and export.

Energy requirement for nuclear transport

Nuclear transport requires GTP hydrolysis from Ran-GTP/GDP for energy.

Targeting signal for nuclear transport

The nuclear localisation signal (NLS) that directs proteins to the nucleus.

Receptor for nuclear transport

Importins alpha/beta that recognize and bind the NLS.

Transport complex for nuclear transport

The nuclear pore complex (NPC) that facilitates the transport of proteins.

Protein state during nuclear transport

Proteins must be in a folded state during transport from the cytoplasm to the nucleus.

Stage of protein transport

The process occurs post-translation.