Session 10 (work group)-Protein Targeting Signals

Question 1

What is the nature of the signal to the ER?

Answer 1

Signal sequence (recognised by SRP during translation)

Question 2

What is the nature of the signal to the nucleus?

Answer 2

NLS=nuclear localising signal
Basic (Arg/Lys)
May be multipartite (having many divisions)

Question 3

What is the nature of the signal to the mitochondria?

Answer 3

Amphipathic signal for initial targeting to the matrix

Question 4

What is the nature of the signal to the lysosomes?

Answer 4

Post-translational addition of mannose-6-phosphate

Question 5

What is the nature of the signal for retention in the ER?

Answer 5

KDEL (Lys-Asp-Glu-Leu)

Question 6

Where is the signal’s location within the primary sequence in the ER?

Answer 6

N-terminus

Question 7

What is the signal’s location within the primary sequence in the mitochondria?

Answer 7

N-terminus (may also be internal “stop transfer”=hydrophobic)

Question 8

Location of signal within primary sequence for retention in ER?

Answer 8

C-terminus

Question 9

Folded or unfolded during transfer:

1. To ER
2. To nucleus
3. To mitochondria
4. To lysosomes
5. Retention in ER

Answer 9

1. Unfolded
2. Folded
3. Held partially unfolded by chaperones
4. Folded
5. Folded

Question 10

What are the specialist proteins involved:

1. To ER
2. To nucleus
3. To mitochondria
4. To lysosomes
5. Retention to ER

Answer 10

1. Signal recognition protein (SRP), SRP receptor
2. Importin recognises NLS and mediates transport; RanGTP displaces it in nucleus and drives out export cargo.
3. Mitochondrial-import stimulating factor ((MSF), Tom and Tim channel complex
4. M-6-P receptor in trans-Golgi
5. KDEL receptor in cis-Golgi

Question 11

Signal retained or cleaved:

1. To ER
2. To nucleus
3. To mitochondria
4. To lysosomes
5. Retention in ER

Answer 11

1. Cleaved by signal peptidase
2. Retained
3. Cleaved
4. Phosphate removed by phosphatase
5. Retained

Question 12

Requires energy?

1. To ER
2. To nucleus
3. To mitochondria
4. To lysosomes
5. Retention in ER

Answer 12

1. Yes-hydrolysis of GTP by SRP
2. Yes-hydrolysis of GTP
3. Yes-ATP hydrolysis by mHsp70 drives translocation; MSF uses ATP to keep some precursors unfolded
4. Yes-phosphotransferase requires ATP (but not direct)
5. No-involves binding and release dependent on pH