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
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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
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3
Q

Capping

A
  • Starts after 20-30 nucleotides
  • Involves 3 reactions, finalised by assoc. of modified cap nucleotide
    1. (RNA triphosphatase carries out 5’ triphosphate → diphosphate)
    1. (guanyltransferase transfers GTP to GMP w/ diphosphate, GMP attached to 1st nucleotide)
    1. (methytransferase uses 5-adenosylmethionie to methylate G at pos 7)
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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
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5
Q

Capping function

A
  • Protects mRNA from degradation by 5’-3’ exonuc
  • Stimulates splicing
  • Nuclear-cytoplasmic export
  • Translation initiation
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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

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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
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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
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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
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