import and export of nucleus

Question 1

The structure of the nuclear pore complex (NPC) consists primarily of a spoke complex:
It has an ______

Answer 1

octagonally symmetric cylindrical structure about 50nm tall around the axis of transport and a planar pseudo-symmetry through the nuclear envelope

Question 2

Attached to the central framework are

Answer 2

8 cytoplasmic filaments and a nuclear basket formed from 8 filaments that join into a distal ring.

Question 3

The linear dimensions of the NPC vary between species, but the ______ is conserved.

Answer 3

3D architecture

Question 4

NPC External diameter is about

Answer 4

125nm

Question 5

The ______ are a family of proteins which are the constituent building blocks of the NPC.

Answer 5

nucleoporins

Question 6

_______ are repetitively arranged in distinct subcomplexes.

Answer 6

About 30 distinct nucleoporins (Nups)

Question 7

There are a total of _____ per NPC.

Answer 7

500-1000 nucleoporins

Question 8

A typical nucleoporin has a domain structure with an N terminus containing _______ and a C terminus rich in ______

Answer 8

multiple copies of the motif XFXFG (FG repeats)

heptad repeats characteristic for coiled-coil conformation.

Question 9

a typical nucleoporin has two domains

Answer 9

N and C terminus

Question 10

There are several models for the NPC permeability barrier to cargo, all of which involve _______:
(4)

Answer 10

FG Nups

1. Selective Phase/Hydrogel Model
2. Virtual Gate/Polymer Brush Model
3. Forest Model
4. Reduction of Dimensionality Model

Question 11

Selective Phase/Hydrogel Model

Answer 11

Barrier is a 3-D sieve formed from inter- and intra-molecular interactions of FG-Nups

Question 12

Virtual Gate/Polymer Brush Model

Answer 12

FG-Nups move vigorously back and forth to create a repulsive barrier with few stable
cohesive contacts

Question 13

Forest Model

Answer 13

1. FG-Nups adopt a mixture of extended (“tree”) and collapsed (“shrub”) conformations.
2. The ends of several “trees” can form cohesive contacts to create a central tunnel
   (zone 1) that acts as a hydrogel, with a second route closer to the walls

(zone 2) acting as a virtual gate

Question 14

Reduction of Dimensionality Model

Answer 14

1. FG-Nups coat the inner surface of the pore to form a hydrophobic surface
2. Hydrophilic unfolded chains extend into the central pore to create a selectivity filter

Question 15

Recent work has shown that nucleoporins pull double duty as.

Answer 15

transcription factors regulating the activity of genes active during early development

Question 16

Nucleoporins don’t regulate all genes, but are required for a subset of genes, including

Answer 16

developmentally regulated genes, which are turned on and off in a controlled manner during cell differentiation and tissue development.

Question 17

NPC components:

Answer 17

The gene doesn’t go to the pore; the pore protein goes to the gene.

Question 18

_______ may also be a potential marker for cancer.

Answer 18

Nucleoporins

Question 19

Nucleoporins ______are highly overexpressed in some cancers, including _______.

Answer 19

Nup214 and Nup88

colon cancer and very aggressive forms of lung cancer

Question 20

Karyopherins are the proteins that

Answer 20

the proteins that actually facilitate nuclear transport through the NPC. The act as mediators between the nuclear pore complex and the cargo being transported.

Question 21

Karyopherins may act as

Answer 21

importins or exportins, and are part of the Importin-β super-family which all share a similar three-dimensional structure.

Question 22

Karyopherins are ______ molecules composed ______

Answer 22

heteromeric

two major types of components, alpha karyopherins and beta karyopherins, that function together to transport molecules through the NPC.

Question 23

Beta-karyopheryins

Answer 23

receptor family of karyopherins

directly interact with FG Nups
Some also interact directly with cargo

Question 24

Alpha karyopheryins

Answer 24

adaptor family of karyopherins

facilitate cargo selective binding

Question 25

Several other proteins such as _____ and _____ bind to karyopherins and participate in the transport process.

Answer 25

Ran GTP binding protein and cellular apoptosis susceptibility protein

Question 26

Ran is a:

Answer 26

(RAs-related Nuclear protein) small 25Kda protein that is involved in transport into and out of the cell nucleus.

Question 27

Ran is a member of the ____ family

Answer 27

Ras superfamily.

Question 28

Ran is a ______ protein that is essential for the ______

Answer 28

GTP binding translocation of RNA and proteins through the NPC.

Question 29

Ran exists in the cell in two nucleotide-bound forms:

Answer 29

GDP-bound and GTP-bound.

Question 30

RanGDP is converted into RanGTP through the action of

Answer 30

regulator of chromosome condensation 1 | (RCC1), the nucleotide exchange factor for Ran.

Question 31

Ran's intrinsic GTPase-activity is activated through interaction with ______, facilitated by complex formation with _____

Answer 31

Ran GTPase activating protein (RanGAP), Ran-binding protein (RanBP).

Question 32

GTPase-activation leads to the conversion of _____, thus closing the Ran cycle.

Answer 32

RanGTP to RanGDP

Question 33

Ran can diffuse freely within the cell, but because RCC1 and RanGAP are located in different places in the cell, the concentration of

Answer 33

RanGTP and RanGDP differs locally as well, creating concentration gradients that act as signals for other cellular processes.

Question 34

RCC1 is located ______

Answer 34

inside the nucleus

Question 35

RanGAP is bound to _____

Answer 35

the nuclear envelope I

Question 36

This difference in location of the accessory proteins in the Ran cycle leads to

Answer 36

a high RanGTP to | RanGDP ratio inside the nucleus and an inversely low RanGTP to RanGDP ratio outside the nucleus

Question 37

RanGTP =

Answer 37

nuclear export

Question 38

In addition to a gradient of the nucleotide bound state of Ran, there is a gradient of the protein itself, with a higher concentration of_____

Answer 38

Ran in the nucleus than in the cytoplasm

Question 39

Cytoplasmic RanGDP is imported into the nucleus by _______

Answer 39

the small protein NTF2 (Nuclear Transport Factor 2),

Question 40

in the nucleus, RCC1 can then catalyze exchange of______

Answer 40

GTP for GDP on Ran

Question 41

Ran is involved in the transport of

Answer 41

proteins across the nuclear envelope by interacting with karyopherins and changing their ability to bind or release cargo molecules.

Question 42

Cargo proteins containing a NLS are bound by

Answer 42

importins and transported into the nucleus o Inside the nucleus, RanGTP binds to importin and releases the import cargo

Question 43

Cargo that needs to get out of the nucleus into the cytoplasm binds to

Answer 43

exportin in a | ternary complex with RanGTP

Question 44

Upon hydrolysis of RanGTP to RanGDP outside the nucleus, the complex

Answer 44

dissociates and export cargo is released

Question 45

Nuclear localization signal and human disease:

Answer 45

1. Male to female sex reversal | 2. Cowden Syndrome

Question 46

Male to female sex reversal –

Answer 46

1. XY female with external feminine genitalia but a lack of formation of both ovaries and testes 2. Normally Importin Beta 1 binds to SRY to translocate to the nucleus, where it can upregulate transcription of target genes 3. If SRY lacks an NLS, it will not be translocated to the nucleus and male sex determining genes will not be transcribed, resulting in male to female sex reversal

Question 47

Cowden Syndrome

Answer 47

1. Autosomal dominant disease with high susceptibility to multiple hamartomas affecting derivatives of all three germ layers and by an increased risk of breast, thyroid, and endometrial neoplasia 2. Protein of interest is PTEN, which is normally translocated by Kapβ o If no NLS, will not enter nucleus

Question 48

Nup Fusions in Cancer:

Answer 48

1. NUP98/HOX fusions in acute myeloid leukemia (AML) | 2. Aberrantly induces transcription of downstream HOX genes

Question 49

Role of NPC in Aging:

Answer 49

1. No new NPCs are produced in post-mitotic cells 2. This makes them prone to oxidative damage 3. The result is a leaky nuclear pore 4. This is seen in aging

Question 50

inhibiting nuclear translocation of calcineurin can prevent

Answer 50

myocardial hypertrophy.

Question 51

Nucleoporin: Human Nup 155 | Tissue specific disorder:

Answer 51

Af, which is a cardiac disorder characterized by clinical arrhythmia

Question 52

Nucleoporin: Human Nup98 | Tissue specific disorder:

Answer 52

Acute myeloid leukemia (and other hematological malignancies) haematopoeitic stem cell proliferation

Question 53

Nucleoporin: Human Nup62 | Tissue specific disorder:

Answer 53

primary bilary cirrhosis (autoimmune liver degen) for autoimmune antigen mutation OR Aitsomal recessive infantile bilalteral striatal necrosis (degeneration of the basal ganglia) for the homozygous missense Q391P mutation

Question 54

Nucleoporin: Human Nup358/RanBP2 (-) | Tissue specific disorder:

Answer 54

Familial cases of infection triggered acute necrotizing encephaly

Question 55

Nucleoporin: Human Nup 155 Mutation:

Answer 55

homozygous missense R391H

Question 56

Nucleoporin: Human Nup98 | Mutation

Answer 56

multiple genomic translocations, which results in fusion of Nup98 fragment, including FG repeats to another gene

Question 57

Nucleoporin: Human Nup 62 Mutation:

Answer 57

autoimmune antigen or homozygous missense Q391P mutation

Question 58

Nucleoporin: Human Nup358/RanBP2 (-) mutation:

Answer 58

heterozygous missense mutation T585M

Question 59

three layers of the NPC

Answer 59

1. membrane 2. scaffold 3. barrier

Question 60

the layer that is functional s the

Answer 60

barrier layer. this acts as the selective gate

Question 61

the scaffold layer provides the

Answer 61

curvature of the NPC

Question 62

_____ in, ____ out

Answer 62

NLS | NES

Question 63

Ran.GTP:Importin/Exportin binding is _____, and blocks ______; _____ relieves this block allowing ______

Answer 63

very tight Ran’s intrinsic GTPase activity RanBP1 RanGAP1 to activate Ran’s intrinsic GTPase by up to 105 fold

Question 64

_____ not cleaved during transport, so can be re-used

Answer 64

NLS/NES

Question 65

The translocation channel is a proteinaceous pore lined by

Answer 65

natively unfolded proteins that use hydrophobic interactions to form a selective filter.

Question 66

ImporVn α an _____

Answer 66

adapter protein: | > 7 family members in humans

Question 67

ImporVn β the

Answer 67

cargo carrier: >20 family members involved in both import and export, many members do not require an adapter protein

Question 68

Proteins (or protein complexes) may shuttle: contain both

Answer 68

NLS and NES

Question 69

Ran accounts for ___% of total cell protein

Answer 69

0.4% total cell protein ≈107 copies/cell

Question 70

The signals are typically exposed linear sequences of amino acids, often containing _____

Answer 70

multiple basic and/or hydrophobic residues. | They are not cleaved following transport.

Question 71

cargo transporters are generally members of the ____ family.

Answer 71

karyopherin

Question 72

Transport is regulated by the

Answer 72

1. entropy barrier created by the Nups, 2. the presence of the Ran.GDP/GTP gradient, 3. the interaction of cargo transporters with nucleoporins, and 4. cargo modifications/interactions that impact association with receptors.

Question 73

Diseases occur when proteins are

Answer 73

mislocalized, either because the selectivity barrier is compromised, or mutations perturb key interactions.