mRNA turnover

Question 1

How does polyA tail length affect mRNA stability?

Answer 1

Length of polyA tail decreases over time due to deadenylases.
Once shorter than roughly ten bases = PABP can no longer bind = degradation

Question 2

how are mRNA stability and translational efficiency related?

Answer 2

inversely correlated

Question 3

What are the rate limiting steps of mRNA decay

Answer 3

Deadenylation and decapping

Question 4

How does DCP1/DCP2 complex remove m7g cap from mRNA

Answer 4

hydrolyses 5’-5’ triphosphate linkage releasing m7GDP cap

Leaves 5’monophospate group on RNA

Question 5

What are AREs?

Answer 5

AU Rich Elements in 3’ utr of unstable mRNAs

Question 6

Which factors can positively and negatively regulated ARE mediated decay?

Answer 6

\+ve = AUF1
-ve = HUR

Question 7

What is the purpose of miRNAs in mRNA processing?

Answer 7

Direct post translational modification of most human mRNAS.

Anneal to sites usually in 3’ UTR of mRNA

Question 8

What is an example of an miRNA?

Answer 8

RISC complexes are miRNAs which can cleave target mRNAs and recruit deadenylases to repress translation

Question 9

Discuss degradation of mRNAs by Nonsense-mediated decay pathway

Answer 9

Alternative splicing of nonsense mutations on translation can cause mRNAs with early stop codons - degraded by NMD pathway
NMD is triggered by absence of interactions between 3’RNP and ribosomes as there are no 3’RNP 3’UTR complexes on truncated mRNA

Question 10

If stable and unstable RNAS are under the same transcriptional control, which will accumulate more?

Answer 10

stable RNAS

Question 11

If transcription rate of RNA changes, what type of RNA will be first to reach new steady state?

Answer 11

Unstable RNAs

Question 12

What is the motif found in ARE mediated mRNAs?

Answer 12

AUUUA