BI203 Lecture 16: The Nucleus - Transport Across the Nuclear Envelope

Question 1

Proteins that must enter the nucleus have amino acid sequences called ____ ____ ____.

Answer 1

nuclear localization signals

Question 2

Nuclear localization signals are recognized by ____ ____ ____.

Answer 2

nuclear transport receptors

Question 3

Nuclear localization signals are rich in ____ amino acids.

Answer 3

basic

Question 4

Nuclear localization signals can be ____ - Composed of amino acid sequences separated by non-NLS amino acids.

Answer 4

bipartite

Question 5

Nuclear localization signals can be composed of amino acid sequences separated by ____ amino acids.

Answer 5

non-NLS

Question 6

_____ = a family of proteins that bind NLS’s & transport proteins into the nucleus.

Answer 6

importins

Question 7

Nuclear localization signals were first identified in 1984, using a viral replication protein ____ ____ _____.
The amino acid sequence responsible for nuclear localization was determined using ____ ____ mutants.
When the same sequence was attached to other proteins, they were also transported to the ____.

Answer 7

SV40 T antigen, T antigen, nucleus

Question 8

The T antigen nuclear localization signal is a ____ stretch of amino acids. Other signals are bipartite.

Answer 8

single

Question 9

Four nuclear proteins with basic amino acids in their NLS Sequences.

Answer 9

T antigen, p53, Egr1, GATA

Question 10

Nuclear localization signals (NLS) are recognized by receptors called ____ which carry proteins through the nuclear pore complex.
____ work in conjunction with the GTP-binding protein ____, which controls directionality of movement.

Answer 10

importins, Ran

Question 11

1) Proteins destined for a particular subcellular location will contain a common amino acid sequence “tag”

For nuclear proteins = ____ ____ ____ (NLS).

2) That “tag” will be recognized & bound bind a “transporter” protein

For nuclear proteins = ____.

3) That “transporter” protein will mediate transport its “cargo” to its destined location.

Answer 11

nuclear localization signal, importins

Question 12

Key Point: Importins bind to the ____ of a protein, then to ____ ____ ____ and the complex is transported across the membrane.

Answer 12

NLS, nuclear pore proteins

Question 13

Importins then interact with the ____ ____ of the nuclear pore complex, which directs transport of the importin/cargo complex into the nucleus.

Answer 13

cytoplasmic filaments

Question 14

Nuclear transport by importins is controlled by the GTP-binding protein ____.

Answer 14

Ran

Question 15

____/____binds to the importin, and this complex is transported back.
In the cytoplasm, ____ ____ hydrolyzes the GTP on Ran to GDP, releasing the importin.
The ____/____ formed in the cytoplasm is then transported back to the nucleus by its own import receptor, where Ran/GTP is regenerated.

Answer 15

Ran/GTP, Ran GAP, Ran/GDP

Question 16

Ran GEF = ?

Answer 16

Ran GTP Exchange Factor (activator of Ran)

Question 17

Ran GAP = ?

Answer 17

Ran GTPase Activating Protein (deactivator of Ran)

Question 18

Ran also controls nuclear ____ of proteins via regulation of ____ trafficking.

Answer 18

export

Question 19

1) ____ bind NLS & transport cargo protein through the nuclear pore complex.
2) Binding of ____/____to importin dislodges cargo protein.
3) Ran/GTP transports importins back ____ of nucleus.
4) Conversion of Ran/GTP to Ran/GDP by ____ ____ releases importin.

Answer 19

Importins, Ran/GTP, out, Ran GAP

Question 20

1) Proteins destined for nuclear export contain a ____ ____ ____ (NES).
2) NES’s are recognized & bound by ____.
3) Binding of ____/____ stabilizes the complex & transports it out of the nucleus.
4) Conversion of Ran/GTP to Ran/GDP by ____ ____ releases cargo protein.

Answer 20

nuclear export signal, exportins, Ran/GTP, Ran GAP

Question 21

Many importins & exportins are members of a family of nuclear transport receptors called ____.

Answer 21

karyopherins

Question 22

Exportins transport ____, ____, and ____.

Answer 22

tRNAs, rRNAs, miRNAs

Question 23

RNAs are transported to the cytoplasm as ____ ____ (RNPs).

Answer 23

Ribonucleoprotein complexes

Question 24

____ transport does NOT involve karyopherins and is independent of Ran. A distinct transporter complex moves the ____ through the nuclear pore. ____ on the cytoplasm side releases the ____ and ensures unidirectional transport.

Answer 24

mRNA, Helicase

Question 25

Regulation of the ____ and ____ of transcription factors is a way of controlling gene expression.

Answer 25

import, export

Question 26

Two examples of regulated gene expression through controlled access of transcription factors to the nucleus:

Answer 26

NF-kB, Pho4

Question 27

The transcription factor NF-kB is regulated by ____ ____, while the yeast transcription factor Pho4 is regulated by ____.

Answer 27

protein-protein interactions, phosphorylation

Question 28

NF-kB is regulated by protein-protein interactions with ____. When phosphorylated, ____ degrades and dissociates, allowing NF-kB’s ____ to be read (NF-kB can now be imported).

Answer 28

lkB, NLS

Question 29

Pho4 has its NLS blocked when ____. When ____, its NLS can be read, and a(n) ____ can transport it.

Answer 29

phosphorylated, dephosphorylated, importin