Lecture 7- Nuclear transport of macromolecules

Question 1

what are nuclear lamina

Answer 1

part of the cytoskeleton attached to the inner nuclear membrane

Question 2

some functions of the nuclear membrane (6 here)

Answer 2

○ Barrier- separation of genome
○ Chromatin organisation
○ Nucleus localisation and migration
○ Gene expression
○ Post-transcriptional quality control
Control of nuclear content

Question 3

different ways molecules can move across the nuclear membrane

Answer 3

diffusion
nuclear envelope budding involving movement through both layers
through pore complexes- can be passive or active

Question 4

basic structure of the nuclear pore

Answer 4

central part is symmetrical and has 8-way rotational symmetry, the filaments are different on either side
anchored to the membrane by transmembrane proteins
pore centre has dynamically changing proteins which are hard to define

Question 5

FG NUPs- what are they

Answer 5

FG nucleoporins, exist in the central pore and have low hydrophobicity and charge, have dynamic binding which allows molecules to move through slowly as conformation changes

Question 6

what facilitates bidirectional transport

Answer 6

presence of both nuclear basket and cytoplasmic filaments

Question 7

what allows directionality

Answer 7

asymmetric parts of the basket and filaments, such as docking sites or proteins which aid in transport complex disassembly

Question 8

examples of dynamic behaviour of nuclear pores

Answer 8

number and size are variable depending on cell type, metabolic state etc, differences in distribution to aid functionality

Question 9

protein transport receptors

Answer 9

karyopherins- RNA can also use these but they more often use NXT1/NFT2

Question 10

protein import receptors

Answer 10

importin beta receptors

Question 11

what are the sorting signals on gargo proteins

Answer 11

nuclear localisation signals, can be ‘classical’ or ‘PY-NLS’s with different amino acid makeups and therefore interactions

Question 12

what is the role of Ran GTPase

Answer 12

induction of transport complex disassociation following activation by RanGEF

Question 13

in what way is nuclear transport energy dependent

Answer 13

GTP hydrolysis is required for replenishing RanGTPase, which facilitates breakdown of transport complexes and therefore continuation of the process

Question 14

sorting signals in export

Answer 14

niclear export signal NES binds to karyopherin receptors in the nucleus called exportins cause RanGTPase-mediated complex breakdown

Question 15

how does mRNA export differ

Answer 15

generally Ran-independent, using a heterodimeric receptor complex instead- but can be Ran-dependent using a similar mechanism

Question 16

examples of proteins with which mRNA forms a complex with during transpoer to aid packaging

Answer 16

exon interactome, CBC of CBPs at the 5’ end to help modify the cap

Question 17

what is NXF1-NXT1

Answer 17

receptor which binds to the TREX complex on the mRNA, docks to the nucleaer basket for quick translocation

Question 18

examples of proteins involved in the cytoplasmic remodelling of the mRNA-protein (mRNP) complex

Answer 18

Gle1, hydrolyses Dbp5 which is attached to the mRNA, which induces NXF1 dissociation

Question 19

how does budding work

Answer 19

disassembly of the local lamina, inner membrane can be distorted by membrane coat molecules to allow docking and budding
vesicles can fuse to the outer membrane from the outside