Nuclear Pore Complexes

Question 1

Nuclear Pore Complex: name as many facts as you can

Answer 1

a) bidirectional
b) molecules utilizing these channels must be between
c) peptides destined for import contain a specific amino acid sequence to which importin alpha/beta attaches to (pro-lys-lys-lys-arg-lys-val)
d) requires atp/gtp
e) peptide sequence destined for export also have coded signal
f) translocation proteins are karyopherins: importin alphabeta and Exportin
g) channels consist of around 30 proteins each
h) have 8 fold symmetry around channel
i) have 8 radiating spokes

Question 2

Importin alphabeta is a ______ that does what? How?

Answer 2

karyopherin: imports marked proteins into the nucleus

It recognizes NLS on the protein

Question 3

Name “loose” steps in protein importation:

Answer 3

1) importin alphabeta recognizes NLS on a given protein
2) translocates protein to nuclear pore
3) importin alphabeta recognized by RAN-GDP
4) complex moves through channel
5) everything released from pore; importin released from protein

Question 4

RCCI

Answer 4

chromatin-bound GP-GTP exchanger, generates RAN-GTP

RAN-GTP associates with exportins

Question 5

RAN-GTP: 4 related movements

Answer 5

Promotes formation of stable complexes between exportins and their cargo proteins

RAN-GTP-exportin protein complex moves through the pore into the cytoplasm

RAN-GBP1 dissociates exportin and cargo protein from RAN-GTP

RAN-GAP converts RAN-GTP to RAN GDP

Question 6

Some bottom line issues about RAN

Answer 6

necessary for both import and export

enzymes for hydrolysis of GTP to GDP are on cytoplasmic side/enzymes for exchange of GDP for GTP are on the nuclear side

Directionality of transport is determined by higher concentration of RAN/GTP in the nucleus