The Transport of Molecules between the Nucleus and the Cytosol

Flashcards covering the structural components of the nuclear envelope, categories of transport signals, the mechanism of the Ran GTPase cycle, and nuclear disassembly during mitosis.

Inner nuclear membrane

A component of the nuclear envelope containing specific proteins that act as binding sites for chromatin and the nuclear lamina.

Outer nuclear membrane

The membrane continuous with the ER membrane, which is studded with ribosomes engaged in protein synthesis.

Perinuclear space

The space between the inner and outer nuclear membranes that is continuous with the ER lumen.

Nuclear pore complexes (NPCs)

Large structures with a molecular mass of about $125\text{ million}$ composed of more than $50$ different proteins called nucleoporins, arranged with octagonal symmetry.

Nucleoporins

The protein subunits that compose the nuclear pore complexes.

FG-repeats

Short amino-acid repeats containing phenylalanine and glycine that line the path through the nuclear pore complexes and serve as binding sites for import receptors.

Nuclear localization signals (NLSs)

Signals found in nuclear proteins, often rich in the positively charged amino acids lysine and arginine, that direct their selective import from the cytosol.

Nuclear import receptors

Members of the karyopherin family that bind to nuclear localization signals and nucleoporins to facilitate the entry of cargo proteins into the nucleus.

Nuclear export signals

Specific signals on macromolecules like ribosomal subunits and RNA that direct their selective transport from the nucleus to the cytosol.

Karyopherins

A gene family encoding nuclear transport receptors, which includes both nuclear import and nuclear export receptors.

Ran GTPase

A monomeric GTPase that provides energy and directionality for nuclear transport by existing in two conformational states depending on whether $GTP$ or $GDP$ is bound.

Ran-GAP (GTPase-activating protein)

A regulatory protein located in the cytosol that triggers $GTP$ hydrolysis to convert Ran-GTP to Ran-GDP.

Ran-GEF (guanine exchange factor)

A regulatory protein located in the nucleus that promotes the exchange of $GDP$ for $GTP$ to convert Ran-GDP to Ran-GTP.

Ran Binding Protein

A cytosolic protein that displaces Ran-GTP from the import receptor, allowing Ran-GAP to trigger $GTP$ hydrolysis.

Nuclear lamina

A meshwork of interconnected protein subunits called nuclear lamins that provides shape and stability to the nuclear envelope.

Nuclear lamins

A special class of intermediate filament proteins that polymerize into a two-dimensional lattice at the inner nuclear membrane.

NF-AT (Nuclear factor of activated T cells)

A gene regulatory protein that transitions from the cytosol to the nucleus upon T-cell activation, controlled by its phosphorylation state.