Transcription. Table 13-1 Structure of RNA polymerases ProkaryoticEukaryotic

Transcription

Table 13-1

Structure of RNA polymerases

Prokaryotic Eukaryotic

Transcription phases

Sigma 70 promoters

Transcription start site

Frequency of nucleotides in various sigma 70 promoters

Table 13-1

Bacterial RNA polymerase holoenzyme

Sigma subunit

Promoter binding by the bacterial RNA polymeraserequires a sigma subunit

Binding of sigma 70 to promoter elements

Carboxy terminal domain Non- template domain

Transcription phases

Sigma 70 promotes melting of DNA by flipping twobases out of the double helix

The open complex and its channels

Models for abortive transcription

The elongation process

Figure 12.13 Genomes 3 (© Garland Science 2007)

Cleavage is promotedby proteins GreA and GreB

The rho protein is required for rho-dependenttermination of transcription in bacteria

Figure 12.7 Genomes 3 (© Garland Science 2007)

Rho-independent transcription termination requires a sequence of dyad symmetry followed by 8 A/T bp

Disruption of the ternary DNA-RNA-RNA polymerasecomplex by a termination stem-loop structure

Table 13-1

Eukaryotic RNA polymerase II promoters are complex

Table 13-2

Initiation of transcriptionat RNA polymerase IIpromoters

The TATA-binding protein bends the DNA

TBP recruits TFIIB to the promoter

TFIIB

TBP

The preinitiation complex interacts with activatorsand chromatin modeling factors via a mediator complex

Mediator complexes consist of many subunits thatprobably interact with different activators

Phosphorylation of the C-terminal domain tail is required for promoter escape of RNA polymerase II

Elongation factors increase the processivity ofRNA polymerases

FACT disassembles and assembles nucleosomesduring transcription

FACT

RNA processing proteins are attached to the CTDtail of RNA polymerase II

Addition of a 5’ cap occurs after promoterescape

RNA processing proteins are attached to the CTDtail of RNA polymerase II

Termination of transcriptionis linked to polyadenylationof transcripts

Two models for termination of transcription in eukaryotes

Table 11.3 Genomes 3 (© Garland Science 2007)

Elements in RNA polymerase I promoters

(RNA polymerase I transcribes rRNA genes)

Elements in RNA polymerase III promoters