18 Questions
Which type of cell has 3 RNA polymerases?
Eukaryotic cells
What group of proteins in eukaryotes recognize promoter elements and load RNA polymerase at the start site?
σ-factors
Which group of factors in eukaryotes are involved in recognizing promoter elements and assembling pre-initiation complex?
General transcription factors
In bacteria, the lac operon is regulated by an activator protein called CAP, which stands for:
Catabolite Activator Protein
Which type of cells regulate gene expression by adjusting enzymatic machinery and structural components to changes in nutritional and physical environment?
Prokaryotic cells
Which type of cells normally synthesize only proteins required for survival under current conditions?
Prokaryotic cells
How does the structure of Eukaryotic RNA polymerases compare to E.coli RNA polymerase?
Eukaryotic RNA polymerases are more complex than E.coli RNA polymerase.
In eukaryotic RNA polymerases, how many large subunits are typically present?
2
What happens to the clamp domain of RNA polymerase II when downstream DNA is inserted?
It opens up.
Which type of RNA polymerase has a unique carboxy-terminal domain?
RNA polymerase II
How does the complexity of eukaryotic RNA polymerases compare to bacterial RNA polymerase?
Eukaryotic RNA polymerases are more complex than bacterial RNA polymerase.
How many smaller subunits are common across two or all three eukaryotic RNA polymerases?
None
Which RNA polymerase synthesizes tRNAs and 5S rRNA?
RNA polymerase III
What is the structure of eukaryotic RNA polymerases compared to prokaryotic RNA polymerases?
Eukaryotic polymerases are multi-subunit complexes
What is the unique feature of carboxy-terminal domain (CTD) of eukaryotic RNA polymerase II?
CTD contains 26 repeats of Tyr-Ser-Pro-Thr-Ser-Pro-Ser
How is the synthesized RNA released in eukaryotic RNA polymerase II?
Through the bridge that closes the clamp domain
What is the role of activator proteins in transcriptional activation?
Promote association of Pol II with elongation factors
What does the crystal structure resolution of yeast RNA pol II reveal?
Yeast RNA pol II has been resolved at high resolution
Study Notes
RNA Polymerases
- Four multisubunit RNA polymerases have a similar overall design
- Eukaryotic RNA polymerases are more complex than E. coli RNA polymerase
- Eukaryotic RNA polymerases contain two large subunits and 10–14 smaller subunits
- Some subunits are common between the three eukaryotic RNA polymerases, while others are specific
Structure of RNA Polymerase II
- The clamp domain of RNA Polymerase II (RPB1) opens when downstream DNA is inserted and swings shut during elongation mode
- The shut position anchors the polymerase onto the downstream double-stranded DNA, making it very processive
Transcriptional Activation
- Activator proteins bind to specific transcription-control elements in promoter-proximal sites and distant enhancers
- Activator proteins interact with the multisubunit Mediator complex to assemble general transcription factors and RNA polymerase II (Pol II)
- Pol II initiates transcription, but pauses after transcribing fewer than 100 nucleotides due to the action of NELF (negative elongation factor)
- Activators promote association of the Pol II-NELF-DSIF complex with elongation factor P-TEFb, which releases NELF, allowing resumption of RNA transcription
Eukaryotic RNA Polymerases
- RNA polymerase I synthesizes pre-rRNA
- RNA polymerase II synthesizes mRNAs, small nuclear RNAs, and micro and small interfering RNAs (miRNAs and siRNAs)
- RNA polymerase III synthesizes tRNAs, 5S rRNA, and other small stable RNAs
Unique Features of Eukaryotic RNA Polymerase II
- Eukaryotic RNA polymerase II has a unique carboxy-terminal domain (CTD) on its RPB1 subunit
- The CTD is involved in multiple regulatory interactions, playing a key role in initiation, release, elongation, and processing of synthesized mRNAs
- The CTD contains 26 repeats of Tyr-Ser-Pro-Thr-Ser-Pro-Ser in yeast and 52 repeats in mammals
- Ser residues in the CTD are phosphorylated upon transition from initiation to elongation
Learn about the structural composition of four multisubunit RNA polymerases, with a focus on the differences between eukaryotic and E. coli RNA polymerases. Explore the complex design and specific subunits present in eukaryotic RNA polymerases through space-filling models based on x-ray crystallographic analysis.
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