RNA biology lecture 2 Flashcards
1
Q
Capping overview
A
- Occurs very early elongation just after RNA Pol dis-engaged from promoter
- Cdk7 phosph Pol II Ser 5, Pol II disengages from PIC
- Transcription machinery reconfigured
2
Q
Stage II - arrest of RNAPII
A
- RNAPII stops synthesis after 20-40 bp of RNA
- RNA exits Pol II via exit channel close to CTD
- RNA Pol assoc w. processing factors, DSIF engages Pol by Spt5 interacting w/ Pol near exit channel
- Complex recognised by NELF → RNA pol arrest
- Capping E recruited to CTD
3
Q
Capping
A
- Starts after 20-30 nucleotides
- Involves 3 reactions, finalised by assoc. of modified cap nucleotide
- (RNA triphosphatase carries out 5’ triphosphate → diphosphate)
- (guanyltransferase transfers GTP to GMP w/ diphosphate, GMP attached to 1st nucleotide)
- (methytransferase uses 5-adenosylmethionie to methylate G at pos 7)
4
Q
Capping control
A
- DXO recognises incompletely capped transcript, removes cap + destroys transcript
- Also if methyltransferase x recognise G = substrate for DXO
- If mRNA x bind cap binding complex, exposed ends recognised by decapping E Dep1.2
- Competition btw cap binding complex + DXO or Xin2 binding to cap
5
Q
Capping function
A
- Protects mRNA from degradation by 5’-3’ exonuc
- Stimulates splicing
- Nuclear-cytoplasmic export
- Translation initiation
6
Q
After capping
A
- RNA pol = arrested state, needs to be released
- Cdk9 phosph ser 2 of CTD + subunits DSIF + NELF → rearrangement of transcription complex, TF recruited, RNAP released
7
Q
Promoter proximal stalling importance
A
- Important for capping, allows gene regulation
- Regulation relies on PTEfb, recruited after pausing, causes phosph of Ser CTD
- Chance to activate genes ↑ rapidly
8
Q
pTEfb activation ↑ regulated
A
- Promoter proximal release integrated into signalling pathway
- Recruitment of pTEfb to Pol = RLS
- Activation of pTEFb = subject to ↑ controls
- Most pTEFb = initially inactive, associate w/ HEX1M1, 7SK associates + traps pTEFb inactive
- pTEFb = released due to signals like HIFa, TF, mediator
9
Q
Regulation of gene expression during drosophila development
A
- Embryogenesis, pol II recruited + subsequently paused, genes in permissive state
- Poised Pol II = present across ↑ tissues during pattern formation
- Pause Pol allows activation e.g. upon exposure of cells to gradient of morphogens