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1. BIOL2010- Flow of Genetic Information > BN - Eukaryotic Transcription I > Flashcards

BN - Eukaryotic Transcription I Flashcards

1
Q

How many polymerases are present in Eukaryotic Transcription?

A

RNA Pol I, II, III

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2
Q

What does RNA Pol II require to allow transcription to begin?

A

General transcription factors (equivalent to σ factor)

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3
Q

Why is eukaryotic initiation more complex?

A

Eukaryotic DNA is packaged into nucleosomes

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4
Q

What are the 2 types of core promoters in Eukaryotic Transcription?

A
  1. TATA containing Core promoter
  2. Downstream promoter element (NO TATA)
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5
Q

What makes up the structure of eukaryotic TATA core promoters? (4)

A
  • Enhancer (-1000)
  • Upstream sequence elements USE (-100)
  • TATA box (-30)
  • Initiator (+1)
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6
Q

What are 5 features of the initiator element?

A
  • Simplest functional promoter
  • Can initiate basal transcription in absence of TATA box
  • Conserved Y is pyrimidine
  • Consensus sequence YYANWYY in humans, where, Y = C/T, W = A/ T, N=A/C/G/T, and +1 is underlined.
  • The INR element facilitates binding of TFIID
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7
Q

What are 4 features of the TATA box?

A
  • Conserved sequence TATAAAA
  • Approx 25 bp upstream of initiator
  • Found in ~30% of promoters
  • Core promoter similar concept in Pribnow box (prokaryotes) and TATA box (eukaryotes)
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8
Q

What are the main 2 steps of initiation at the core promoter?

A

1) Need to assemble an RNApol II pre-initiation complex

  • This positions the RNA pol II over transcription start sites

2) General transcription factors for RNA Pol II (TFII) bind to the TATA box

  • The first transcription factor TFIID binds the TATA box
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9
Q

What does TFIID complex consist of?

A

TBP and TAF

  • Involved in binding other TFs to help attach RNAP II to the DNA and attaching proteins that unwind the chromatin structure
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10
Q

What is the order of events of initiation at the core promoter? (5)

A
  1. The first transcription factor TFIID binds the TATA box
  2. TFIIA and TFIIB binds to TFIID
  3. TFIIB then recruits RNApol II to the TATA box.
  4. TFIIF accompanies the RNAPol II and stabilises it
  5. TFIIE and TFIIH bind and make up the initiation complex
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11
Q

What is TFIIH and how does it aid in Elongation?

A

TFIIH

  • A 10 subunit complex containing: ATPase, Helicase, Protein kinase
  • Phosphorylates the C terminal domain of RNApol II and results in release of TFs
  • Helicase activity melts the DNA
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12
Q

What occurs during elongation?

A

Conformation change – RNApol II tightens grip

Acquires new proteins – including elongation factors that help process the RNA and increase elongation rate

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13
Q

How is Cell Fate determined?

A

Cell fate is determined by:

  • Gene expression
  • Cell-cell/cell-matrix interactions
  • External factors e.g. hormones
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14
Q

How can transcription be enhanced?

A

By the binding of transcription factors to sites upstream of the PIC:

  • Upstream sequence elements (USE)
  • GC box and CAAT box - tissue specific enhancement of transcription

These must be in same orientation as the RNA pol II initiation site

  • Upstream position is important
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15
Q

What are 5 features of enhancers?

A
  • Regulatory sequences that act at a distance
  • Cis acting (up to 1Mb away) with reversible orientation
  • Bound by activator proteins
  • These interact with the mediator complex
  • Encourage binding of RNApol II
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16
Q

What are properties of enhancers elements? (3)

A

They can activate transcription when placed thousands of bp away from the TATA box

  • USE cannot be so far away

They act in either orientation

  • USE cannot

Can act when placed upstream or downstream of the TATA box, or when placed within an intron

17
Q

Why may enhancers be lost post-splicing?

A

Enhancers may be found in introns
(Introns are removed during splicing)

18
Q

What are the 3 upstream motifs

A

1. DNA sequence motifs bound by ubiquitous transcription factors

  • e.g., the TF, Sp1 binds to GGGCGG
    Sp1 is found in all cell types

2. DNA sequence motifs that confer tissue specific expression

  • e.g., MyoD binds to CANNTG (N=any base)
    MyoD is a muscle-specific transcription factor
    Note all cells have CANNTG but only tissue specific cells have the MyoD TF expressed.

3. DNA sequence motifs that confer response to particular stimuli

  • e.g., Oestrogen receptor binds to AGGTCANNNTGACCT

1. BIOL2010- Flow of Genetic Information (18 decks)

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