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Chapter 3

BCH311 Andreopoulos.pdf


Department
Biochemistry
Course Code
BCH311H1
Professor
Stavroula Andreopoulos
Chapter
3

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Transcription
Cis= same strand of DNA
Initiation sites and cis-acting elements
Unwind dsDNA
Can transcribe without pausing or primer
1 in 105error (no proofreading)
DNAP: 800 nt/s
RNAP: 50 nt/s
Nucleophilic attack by 3' oxygen to Alpha phosphate
Formation of phosphodiester bonds
Function
E. coli RNAP
400kDa
Core enzyme α2ββ’ has catalytic activity
Released after 10nt- helps find the promoter
σ70 decreases DNA binding affinity
Holoenzyme: α2ββ’σ70
Subunit
Gene
Number
Mass kDa
α
RhoA
2
37
β
RhoB
1
151
β’
RhoC
1
155
σ70
RhoD
1
70
Incoming ribosenucleoside brings in 2nd Mg++
2 metal ions stabilize with 3 Asp residues
Promoter sequences recognized by RNAP
RNA Translation
BCH311 Andreopoulos
BCH311 Page 1

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Initiation
-10 (10nt upstream) conserved: TATAAT (Pribnow Box)
-35 another promoter region
40nt for core promoter
αsubunit helix in promoter recognition
Prokaryote promoter sites
Strong promoters frequent transcription, more substitutions less transcription
17-20nt of conserved sequence
40-60 nts up from start site
C-term αsubunit binds
Upstream elements
BCH311 Page 2

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Rapid and random walking to find promoter
Rate of binding: 1010 /Ms (100x greater)
Release of σcatalytic- super fast
Elongation
Initiation with purine
~8nt before σrelease
1.6 turns of helix
Transcription bubble of 17 bp
1 turn of helix
RNA-DNA hybrid ~8bp long
170A/s or 50nt/s
Nucleotide addition cycle
BCH311 Page 3
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