BN - Polyadenylation Flashcards
Which end of mRNA is polyadenylated and what does this involve?
The 3’ end of the mRNA is polyadenylated
- This involves the addition of a string of Adenosines (~200) to the end of the transcript
- The signal for polyadenylation is encoded in the DNA (conserved 3’ control region)
How is poly-A tail stabilised?
Proteins bind to the poly-A tail (PolyA Binding Proteins (PAB))
What sequences are recognised by what proteins during polyadenylation?
- CPSF (cleavage and polyadenylation specificity factor) binds to AAUAAA region
- Poly A pol binds to CA region
- CstF (cleavage stimulation factor) binds to GU region
- CFI and CFII (cleavage factors I and II) bind to UGUA region
How are these components brought together?
Components brought together by RNAPol II
How do the proteins work together to cleave the RNA? (2)
- CFI and CFII cut downstream of the Poly A pol
- Addition of Poly A tail by Poly A pol
Why is transportation of the long form of RNA preferred?
Easier transportation to cell extremities, allowing protein production where needed
How does RNA leave the nucleus?
Small molecules can move through but larger molecules like RNA and proteins have to be transported across through an energy-dependent process
What ensures only fully spliced RNA is transported through the NPC?
- Exon junction complex (EJC) binds close to the splicing junction by association with the spliceosome.
- After splicing the EJC remains attached to the RNA close to the exon/exon boundary.
- EJC proteins are targeted by Nuclear eXport Factor 1 (NXF1) and Nuclear eXport Transporter 1 (NXT1)
What proteins line the NPC and how do molecules get through?
Nucleoporins or NUPs are GF rich proteins that line the NPC
- All mRNAs are transported through the NPC with the 5’ end going first.
- The proteins involved in transport are returned afterwards back to the nucleus
