Nuclear import and export Flashcards
NE
- perinuclear space (20-50nm)
nuclear lamina
nuclear cytoskeleton attached to lamins
lamins
intermediate filaments
Regulatory NE functions
- gene expression
- QC
- selective control of nuclear content
passive diffusion
- 30-60kDa polar
NPC
- 500-1000 protein
- highly conserved; diameter, abundance, distribution and NUPs vary
Symmetric core
- structural foundation of NPC
- cytoplasmic and nucleoplasmic rings = scaffold NUPs
TM NUPs
anchor NPC to membrane
vesicle coat, adaptin-related NUPs
stabilise membrane shape
FG NUPs
- highly disordered
- low charge, high mean hydrophobicity
selective
phase model
asymmetric
- docking sites for transporter (disassembly) protein complices
protein import
- histones
- lamins
- pols
- TFs
- snRPs
protein export
shuttling
karyopherin
conformational change upon cargo binding increases hydrophobic surfaces
importin-beta
- heat repeat (approx 30-40 residues)
- amphiphilic alpha helix BD rotate
- (importin alpha adaptor protein)
Classical NLS
- short stretch +ve residues (Lys, Arg)
- mono and bipartite
- bioinformatics
multivalent binding
multiple FG NUPs engage with receptor surface
RanGTPase
- low intrinsic activity
- small molecular switch
NES
- 8-15 residue motif
- 4-5 hydrophobic residues (Leu/Val/Ile/Phe/Met) bind groove
- large array
How does RanGDP enter nucleus?
Nft2
bulk mRNA export - the basics
- dimeric
- human: Nfx1-Nxt1
- yeast: Mex62/Mtr2
CBP
- cap binding protein
- promotes splicing
- compacts mRNA
exon interactome
TREX, Dbp5
Dbp5
- DED-box protein 5
- helicase
Bulk mRNA transport - the specifics
- mRNP diffuses from TSS to NPC (rate limiting step: secs/mins)
- TREX, SR recruit Nxf1-Ntx1 (increases RNA affinity)
- mRNP-Nxf1-Ntx1 docks nuclear basket (approx 100ms)
- NPC translocation
- Dbp5 binds Gle1
- ATP hydrolysis; reduced RNA-affinity; Xpo-dissociation
- Nxf1 detaches (80ms)
- protein dissociation during translation and NPC-import
mRNP
mRNA-containing ribonucleoprotein
Nxf1-Ntf1
nuclear RNA export factor 1- ntf2-like export factor 1
Gle1
cytoplasmic filament NUP
Selective mRNA transport
- CRM1
- mRNP
- cd1
- MHC
nuclear envelope budding
- mega RNP granule
- perinuclear vesicles fuse ONM/ER
actively transcribed genes
NPC-adjacent
NPCs and vesicle coating complices
common ancestry
LECA
Ran and karyopherins