Chemistry 21.1-Transcription
Transcript of Chemistry 21.1-Transcription
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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
typeSteady 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 ’
• The ’ subunit is involved in DNA binding
• The subunit contains the polymerase active site
• The subunit acts as scaffold on which the other subunits assemble.
• Also requires -factor for initiation –forms holo enzyme complex
Site of DNA binding and
RNA polymerization
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General Gene Structure5’ 3’Transcribed region terminatorPromoter
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Gene Promoters
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Other -Factors• Standard genes – 70
• Nitrogen regulated genes – 54
• Heat shock regulated genes – 32
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Transcriptional Initiation
Closed complex
Open complex
Primer formation
Disassociation of -factor
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Pausing induces termination
3’end 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 ProductsRNA 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