Chapter 21 (part 1)

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Chapter 21 (part 1)

• Transcription

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Central Dogma
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RNA Content of E. coli Cells
type Steady State Levels Synthetic Capacity Stability
rRNA 83 58 High
tRNA 14 10 High
mRNA 3 32 Very Low
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E. Coli RNA Polymerase

• RNA polymerase core enzyme is a multimeric
  protein a2,b, b, w
• The b subunit is involved in DNA binding
• The b subunit contains the polymerase active site
• The a subunit acts as scaffold on which the other
  subunits assemble.
• Also requires s-factor for initiation forms holo
  enzyme complex

Site of DNA binding and RNA polymerization
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General Gene Structure
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Gene Promoters
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Other s-Factors

• Standard genes s70
• Nitrogen regulated genes s54
• Heat shock regulated genes s32

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Transcriptional Initiation
Closed complex
Open complex
Primer formation
Disassociation of s-factor
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Pausing induces termination
3end tends to be AU rich easily to disrupt
during pausing. Leads to disassembly of RNA
polymerase complex
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Rho Dependent Termination

• rho is an ATP-dependent helicase
• it moves along RNA transcript, finds the
  "bubble", unwinds it and releases RNA chain

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Eukaryotic RNA Polymerases
type Location Products
RNA polymerase I Nucleolus rRNA
RNA polymerase II Nucleoplasm mRNA
RNA polymerase III Nucleoplasm rRNA, tRNA, others
Mitochondrial RNA polymerase Mitochondria Mitochondrial gene transcripts
Chloroplast RNA polymerase Chloroplast Chloroplast gene transcripts
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Eukaryotic RNA Polymerases

• RNA polymerase I, II, and III
• All 3 are big, multimeric proteins (500-700 kD)
• All have 2 large subunits with sequences similar
  to ? and ?' in E.coli RNA polymerase, so
  catalytic site may be conserved

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Eukaryotic Gene Promoters

• Contain AT rich concensus sequence located 19 to
  27 bp from transcription start (TATA box)
• Site where RNA polymerase II binds

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Transcription Factors

• TFAIIA, TFAIIB components of RNA polymerase II
  holo-enzyme complex
• TFIID Initiation factor, contains TATA binding
  protein (TBP) subunit. TATA box recognition.
• TFIIF (RAP30/74) decrease affinity to
  non-promoter DNA