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367 molecular biology > pp 14 > Flashcards

pp 14 Flashcards

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1
Q

What are the three RNA polymerases and what are their functions? (eukaryotes)

A
  1. RNA polymerase I - transcribes precursor to the major rRNA’s
  2. RNA polymerase II - transcribes precursors to mRNA’s called hmRNA and most small nuclear RNA (snRNA)
  3. RNA polymerase III - transcribes precursors for 5S rRNA and the tRNA’s and several small cellular viral RNA’s
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2
Q

Where are the three RNA’s found?

A
  1. nucleolus
  2. nucleoplasm
  3. nucleoplasm
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3
Q

Why is a-amanitin an inhibitor of eukaryotic polymerase II

A

It is strongly inhibited by it, whilst pol III is less and pol I isn’ t at all. When it is added, loss of production of pre-mRNA is seen

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4
Q

How many subunits does bacterial RNA polymerase II have vs eukaryotic?

A

Bac: 5 (w, B, B’, aI, aII)
Euk: 12 (1-12)

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5
Q

What are the role of the core subunits and which ones are they?

A

Rbp1, Rbp2, Rbp3 for the core.
They are essential for enzyme activity and homologous to B’ and B and a subunits of Ecoli.

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6
Q

Which subunits are shared amongst all the three RNA polymerases?

A

RpB 5,6,8,10,12

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7
Q

What factors are needed to recruit RNA polymerases to promoters?

A

general transcription factors (proteins) for the transcription of all class I, II, III genes. they are abbreviated as TFIs, TFIIs, TFIIIs

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8
Q

How do the eukaryotic promoters bind with RNA polymerase?

A

the different polymerases recognize different promoters. Promoter elements attract general transcription factors that then bind polymerases.

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9
Q

What are the elements of the class II core promoters?

A
  • TFIIB recognition element (BRE) : binding site for TFIIB
  • TATA box: binding site for TBP
  • Initiator (inr) : binding site for TFIID
  • Downstream core element (DCE): binding site for TFIID
  • Downstream promoter element (DPE)L: binding site for TFIID subunits
  • motif ten element (MTE): binding site for TFIID subunits
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10
Q

What is the TATA box and what is it used for?

A

A class II promoter element, has a consensus sequence TATAAA, and it binds TBP subunit of TFIID

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11
Q

What is the TFIID and why is it important?

A

It is general transcription factor and is a complex assembly of protein subunits. It has the TATA box-binding protein (TBP) and it also has 13 other proteins called TAF (TBP - associated factors)

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12
Q

How is RNA polymerase II recruited to the promoter for initiation?

A
  1. recruitment beings with TFIID binding promoter. (binds TATA through TBP, can bind to TATA-less through interactions with TAFs)
  2. TFIIA helps TFIID bind to promoter by unmaksing TBP
  3. TFIIB binds after
    4, RNA polymerase II binds through mutual interaction with TFIIF
  4. TFIIE and TFIIH bind to create closed complex
  5. TFIIH has ATP-driven DNA helicase to unwind DNA near transcription site to form open complex
  6. TFIIH also has ATP-dependent kinase to phosphorylate C-terminal domain (CTD) of RNA pol II allowing to clear promoter
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13
Q

What is the transcription process in eukaryotes?

A
  1. Pol II is recruited to DNA
  2. Formation of transcription bubble
  3. Phosphorylation of CTD during initiation
  4. Elongation
  5. Transcription terminates and CTD is dephosphorylated
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14
Q

What happens during step one of transcription?

A

formation of preinitiation complex, TFIIH unwinds DNA, and attaches phosphate groups to CTD of RNA allowing dissociation

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15
Q

What happens during the second and third step of transcription?

A

initiation complex formation
elongation complex is formed

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16
Q

What happens during the fourth step of transcripton?

A

RNA dont transcribe at steady rates, short dtops “transcription pauses” occur as sequences destabilize the RNA-DNA hybid causing backtrack. To recover, TFIIS stimulates RNase activity. Forms termination complex

17
Q

What happens during the last step of transcription?

A

polyadenylation signal sequence (AAUAAA) transcribed. Exonuclease Xrn2 binds to CTD and acts on new 5’. this degrades residual mRNA from 5’ end until it reaches RNA polymerase II, triggering dissociation from template DNA

18
Q

What are enhancers?

A
  • DNA elements that stimulate transcription of a gene that may be distant (upstream activation sequence UAS is enhancer upstream of gene it regulates)
  • Downstream activation sequence (DAS) also is enhancer
  • All class II genes require enhancer UAS or DAS element for expansion
19
Q

What are activators?

A

include proteins that bind to enhancers and help to recruit RNA polymerase to the promoter, stabilizing its binding

20
Q

What are mediators?

A

Multiprotein complex that functions as an intermediary between activators and the pre-initation complex consisting of general transcription factors and RNA polymerase

367 molecular biology (10 decks)

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