Transcription

1. Transcription
By- Dr. Armaan SinghBy- Dr. Armaan Singh

2. Central Dogma

3. 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

4. E. Coli RNA Polymerase
• RNA polymerase core
enzyme is a multimeric
protein α2,β, β’, ω
• The β’ subunit is
involved in DNA
binding
• The β subunit contains
the polymerase active
site
• The α subunit acts as
scaffold on which the
other subunits
assemble.
• Also requires σ-factor
for initiation –forms
holo enzyme complex
Site of DNA
binding and RNA
polymerization

5. General Gene Structure
5’ 3’Transcribed region terminatorPromoter

6. Gene Promoters

7. Other σ-Factors
• Standard genes – σ70
• Nitrogen regulated genes – σ54
• Heat shock regulated genes – σ32

8. Transcriptional
Initiation
Closed complex
Open complex
Primer formation
Disassociation
of σ-factor

10. Pausing induces
termination
3’end tends to be AU
rich easily to disrupt
during pausing. Leads to
disassembly of RNA
polymerase complex

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

13. 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

14. 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
β and β' in E.coli RNA
polymerase, so catalytic
site may be conserved

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

16. 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