RR13

Question 1

What are 4 methods of RNA quality control?
What happens if these don’t work?

Answer 1

• SR proteins
• Polyadenylation of pre-mRNA
• Export factors are loaded onto mRNA
• Remaining factors must be removed in pioneering round of translation

If these don’t work- there are other issues: Nonsense mediated decay

Question 2

What is nonsense mediated decay

Answer 2

Process of mRNA surveillance to ensure that in frame stop codons are eliminated

We have nuclear proteins bound to exons, they make their way through pore
An in frame stop codon - ribosomes will only get midway through

Question 3

What pattern is often found in short-lived mRNAs?

Answer 3

• AuuuA or other repetitive elements on UTR
  they destabilize mRNA

Question 4

What is the exosome?

Answer 4

A complex that works by degradin mRNA before carrying out it’s actual function (deadenylation of polyA tail)
3’-5’ decay

Question 5

What is the degradation of 5’ end consist of?

Answer 5

decapping with XRNI
5’ -> 3’ decay

Question 6

Which end does RNA decay take place?

Answer 6

• Can occur at both ends!
• sometimes cleaved in the middle, then degraded by both exonucleolytic pathways

Question 7

What is the TfR?

Answer 7

The mammalian transferrin receptor
- it is regulated in response to iron concentration
- Has stem loops in untranslated region
- Iron response element binding protein

• Active in low iron, protects mRNA and blocks proteins from creating more Tfr
• Inactive in high iron, tFr mRNA is degrading and unstable

Question 8

How is mRNA related to protein levels?

Answer 8

mRNA abundance almsost always reflects protein levels
- Can be skewed, it may indicate that protein synthesis or stability is being regulated

Question 9

Explain drosophila development and mRNA translation

Answer 9

• drosophila larva mRNA has a uniform distrobution, but the hunchback protein has a very steep anterior to posterior gradient:
• 2 hunchback genes at anterior
• 1 nanos at posterior
• The protein is made in posterior, showing that mRNA is not linked to protein levels. Without nanos, protein is made across entire larva, which is lethal

Nanos ensures that hunchback is only translated in the anterior

Question 10

How is FERRITIN regulated?

Answer 10

Ferritin is a protein that binds irons ions, preventing it’s toxic accumulation
In low iron systems, IRE-BP binds to 5’ UTR of ferritin, inhibiting translation

Question 11

Explain the C.elegans mutation and what we have learned from it

Answer 11

• Mutant in C.elegans, causes it to never leave it’s larval stage.
• Found that lin4 is blocking the translation of lin14, causing the lin 14 to repeat first larva stage due to lack of 3’ UTR

This was the discovery of the microRNAs - which control more than 60% of our genes