What are 4 methods of RNA quality control?
What happens if these don’t work?
- 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
What is nonsense mediated decay
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
What pattern is often found in short-lived mRNAs?
- AuuuA or other repetitive elements on UTR
they destabilize mRNA
What is the exosome?
A complex that works by degradin mRNA before carrying out it’s actual function (deadenylation of polyA tail)
3’-5’ decay
What is the degradation of 5’ end consist of?
decapping with XRNI
5’ -> 3’ decay
Which end does RNA decay take place?
- Can occur at both ends!
- sometimes cleaved in the middle, then degraded by both exonucleolytic pathways
What is the TfR?
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
How is mRNA related to protein levels?
mRNA abundance almsost always reflects protein levels
- Can be skewed, it may indicate that protein synthesis or stability is being regulated
Explain drosophila development and mRNA translation
- 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
How is FERRITIN regulated?
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
Explain the C.elegans mutation and what we have learned from it
- 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
