Nuclear Transport Flashcards
Components of the nuclear envelope (3)
- Inner nuclear membrane
- Outer nuclear membrane
- Perinuclear space
Inner nuclear membrane
Contains sites for chromatin anchoring & nuclear lamina
Outer nuclear membrane
Continuous with ER membrane. Studded with ribosomes on its outer face
Perinuclear space
Located between the inner and outer membranes. This is also called the ER lumen
Nuclear pores
The double-membrane envelope is penetrated by pores in which nuclear pore complexes are positioned
Nuclear pore complex (NPC)
Protein complexes that perforate the nuclear envelope in eukaryotes. Each NPC is composed of 30 different proteins (nucleoporins). The nucleoporins are arranged as octagons, creating a central pore. One nuclear envelope can contain 3000-4000 NPCs.
Central pore
The pore formed by nucleoporins in NPCs. This is water filled channel that provides free passage for small water soluble molecules under 5,000 Da. Larger molecules travel through more slowly, paying a “toll”. Since many NPCs line the central pore, they block the passage for large molecules
How do large molecules travel through NPCs?
They are ferried across when they bind certain receptor proteins
Nuclear localization signals (NLS)
Short amino acid signals that are covalently attached to proteins destined for the nucleus. The sequences are rich in positively charged amino acids lysine and arginine. The signals are located anywhere on the amino acid and are thought to form loops or patches on the protein surface
Nuclear export signals (NES)
Composed of 4 hydrophobic residues (usually leucine)
Nuclear import receptors
Soluble receptors that bind proteins and transport them as cargo. Binds proteins with a specific NLS and phenylalanine-glycine (FG) domains on the NPC interior
Nuclear export receptors
Binds NES & FG repeats on NPC interior
Why are NLS and NES sequences important?
They are necessary in order to get the correct proteins into/out of the nucleus.
