Genetics 12

Question 0

Nuclear localization signals

Answer 0

• specific AA signal sequences in proteins targeted to nucleus.
• usually sequences of basic AA (lysine or histidine) found on proteins translated by soluble ribosomes.
• Critical role in nuclear transport.

Question 1

In order to activate or repress transcription, a TF must be…

Answer 1

1) located in the nucleus

2) bound to DNA and/or interacting with basal transcriptional apparatus

Question 2

Oily spaghetti model

Answer 2

Nuclear pore may allow small molecules to freely diffuse through due to arrangements of proteins rich with Nsp-1 repeats within the nuclear pore that form a gel-like matrix

Question 3

To be recognized by its chaperone and enter the nucleus, a protein must…

Answer 3

Express a proper nuclear localization signal.

If there is a mutation in the NLS that prevents recognition, protein cannot enter, and will accumulate in cytoplasm.

Question 4

Nuclear importer receptors

Answer 4

AKA importins

-Proteins that recognize NLS and facilitate transport across nucleus

Question 5

Ran

Answer 5

• Monomeric G protein that regulates transport across nuclear envelope.
• regulation is similar to Ras monomeric G protein pathway.
• Has specific GEF and GAP protein, cycles between inactive and active state.
• Ran, GEF, and GAP are localized to regulate directionality.

Question 6

Ran-Gap is ____ whereas Ran-GEF is _____

Answer 6

Cytoplasmic, nuclear

GTP in nucleus encourages active Ran there, GDP in cytoplasm encourages inactive Ran there.

Question 7

Role of Ran in transport

Answer 7

• After nuclear protein/cargo binds its importin, it is transported into nuclear environment. Still able to bind importin.
• GTP-Ran can bind competitively for the importin’s NLS binding site, allowing cargo to dissociate into the nucleus.
• Binding of GTP-Ran to importin stimulates transport back through nuclear pore and into cytoplasm. GTP-Ran enounters GAP–> GDP.
• Inactive GDP-Ran dissociates. Rejuvenating free importin.
• Ran-GDP returns to nucleus, is activated by GTP-Ran by GEF.

Question 8

Role of Ran in nuclear export

Answer 8

Forms trimeric complex between Ran-GTP, the protein with the nuclear export signal, and the nuclear exporter.

• Ran-GTP-exporter-protein complex passes through nuclear pore into cytoplasm.
• GAP activates GTPase activity of Ran–> GTP to GDP. Complex dissociates.

Question 9

All nuclear bound proteins must have a

Answer 9

Nuclear localization sequence (NLS)

Question 10

T/F DNA binding is the most important part of transcriptional regulation

Answer 10

False. Transactivation is more important.