Yeast Lecture 4

Question 1

What is ubiquitin used for?

Answer 1

As a degradation signal, DNA damage repair signal, Transport signal

Question 2

What is the N-end rule

Answer 2

Ub-X-Reporter: DUBs cleave after gly-Gly motive except if followed by Proline. Leaving behind a specific N-End

Question 3

What are some prerequisites for degradation of proteins (also via N-end rule)

Answer 3

N-terminus and suitable lysine residue must be sufficiently exposed

Question 4

What are proteasome mutants sesitive to?

Answer 4

Proteotoxic stress caused by for example heat

Question 5

Why does Ub need to be processed before conjugation?

Answer 5

It is translated as part of the ribosomal subunits and needs to be cleaved off first before conjugation

Question 6

N-end rule ubiquitination

Answer 6

Uba1 (E1) binds Ub with ATP usage
RAD6 gets ubiquitin (E2)
RAD6 binds to UBR1
proteins bearing degrons bind to UBR1 and get ubiquitinated
But UBR1 can also bind other proteins

Question 7

What is a temperature controlled degron?

Answer 7

Degron which only exposes its Lysin sufficiently in high temp and is degraded only then even though it has a sufficiently exposed N-end rule degron at all times

Question 8

Give me some proteasome inhibitors

Answer 8

MG132, Bortezomib

Question 9

RPN4 feedback loop explained

Answer 9

Rpn4 normally always degraded.
Now under stress a lot of proteins accumulate and proteasome cant keep up.
Degradation of RPN4 is stalled and it can go to nucleus where it upregulates proteasome expression