Mechanism of Transcription Chapter 12 Mechanism of Transcription 4 and 6 October, 2006
Overview Transcription is superficially similar to replication, with important differences. E. coli RNA polymerase core has an a2bb’w subunit structure. In Eukaryotes, RNA Pol II transcribes most genes. Transcription consists of initiation, elongation, and termination. Initiation occurs at promoters, which are recognized by the s subunit and the a-CTD in bacteria. Promoter strength depends on a close match to the consensus sequence. Promoter binding is followed by a transition to the open complex. RNA polymerase transition to elongation phase involves abortive initiation. Termination is mediated by signals in the RNA. In Eukaryotes, promoters contain binding sites for TFIID, TF2B, and TBP. Initiation involves a multiprotein assembly at the promoter. Elongation is stimulated by elongation factors, and involves the recruitment of capping, splicing, and polyadenylation proteins. PolI and PolIII promoters are distinct, but require TBP.
Transcription and RNA Polymerases
RNA Polymerase Structure
Events in Transcription
s70 Recognizes Bacterial Promoters
Core polymerase binding is enhanced by sigma and increased temperature.
Promoter Consensus
Polymerase Binding
a-CTD contacts the UP element.
a-CTD contacts the UP element.
RNA Pol Active Site and Channels
RNA Polymerase melts -9 to +3
The b subunit contains the active site.
Termination
Termination
Rho
Three Eukaryotic RNA Polymerases
Eukaryotic Promoter
SV40 Early transcription starts at the same position relative to the TATA box.
Subunit Structure of Pol II
PolII Initiation
General Factor Order of Addition
TBP Minor Groove Interactions
TBP Binding
TBP Recruits TFIIB
TFIID is complex
Roles of TFIID Components
Activation by SP1 requires TAFII-110
TFIID interacts with activators.
Binding of TFIIE
Phosphorylation of the Preinitiation Complex
TFIIH Phosphorylates RNA Pol II
TFIIH Helicase Activity
Promoter Clearance
Transcriptional Initiation with Mediator Complex
Mediator
Elongation
Cap Structure
Polyadenylation and Termination
Pol I Promoter
Pol III Promoter
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