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What is the subunit that recognizes promoter sequences on DNA in prokaryotic RNA polymerase?
What is the subunit that recognizes promoter sequences on DNA in prokaryotic RNA polymerase?
Prokaryotic transcription is less accurate than eukaryotic transcription.
Prokaryotic transcription is less accurate than eukaryotic transcription.
False
What are the two consensus sequence elements found in prokaryotic promoters?
What are the two consensus sequence elements found in prokaryotic promoters?
The -35 region (TTGACA) and the Pribnow box (-10 region, TATAAT).
In prokaryotic transcription, initiation site prefers to bind _____ and _____ for the synthesis of RNA.
In prokaryotic transcription, initiation site prefers to bind _____ and _____ for the synthesis of RNA.
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What is the elongation rate of RNA polymerase during transcription?
What is the elongation rate of RNA polymerase during transcription?
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The termination of transcription in prokaryotes only occurs via specific sequences.
The termination of transcription in prokaryotes only occurs via specific sequences.
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What role does Rho play in prokaryotic transcription termination?
What role does Rho play in prokaryotic transcription termination?
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During chain elongation, _____ precede and follow the RNA polymerase to relieve supercoiling.
During chain elongation, _____ precede and follow the RNA polymerase to relieve supercoiling.
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Match the following elements to their corresponding functions in prokaryotic transcription:
Match the following elements to their corresponding functions in prokaryotic transcription:
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What is the significance of the error rate in prokaryotic transcription?
What is the significance of the error rate in prokaryotic transcription?
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What is the elongation rate of RNA polymerase during transcription?
What is the elongation rate of RNA polymerase during transcription?
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The Pribnow box is located in the -35 region of prokaryotic promoters.
The Pribnow box is located in the -35 region of prokaryotic promoters.
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What are the two binding sites for NTPs in RNA polymerase?
What are the two binding sites for NTPs in RNA polymerase?
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In prokaryotic transcription, the termination factor protein is called _____ and it is an ATP-dependent helicase.
In prokaryotic transcription, the termination factor protein is called _____ and it is an ATP-dependent helicase.
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Match the components of RNA polymerase to their functions:
Match the components of RNA polymerase to their functions:
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What is the primary sequence found in the -35 region of prokaryotic promoters?
What is the primary sequence found in the -35 region of prokaryotic promoters?
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Topoisomerases are involved in the chain termination phase of transcription.
Topoisomerases are involved in the chain termination phase of transcription.
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Describe one mechanism of transcription termination in prokaryotes.
Describe one mechanism of transcription termination in prokaryotes.
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The _____ region helps in the unwinding of the DNA during transcription initiation.
The _____ region helps in the unwinding of the DNA during transcription initiation.
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What is the primary role of the sigma subunit in prokaryotic transcription?
What is the primary role of the sigma subunit in prokaryotic transcription?
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Study Notes
Transcription in Prokaryotes
- Prokaryotes have a single RNA polymerase.
- E. coli's RNA polymerase is a complex of ~465 kD with five subunits: 2 α, 1 β, 1 β', 1 ω.
- α subunits bind DNA.
- β subunits bind NTPs and interact with ω.
- ω recognizes promoter sequences on DNA.
- β' subunits are essential for assembly and activation of the enzyme by regulatory proteins.
- Prokaryotic RNA polymerase has a low error rate of about 1 in 10,000 bases.
- This error rate is acceptable as many transcripts are made from each gene.
- E. coli's RNA polymerase is a complex of ~465 kD with five subunits: 2 α, 1 β, 1 β', 1 ω.
Stages of Transcription
- There are four stages of transcription:
- Initiation: RNA polymerase holoenzyme binds to promoter sites.
- Polymerization: The enzyme initiates polymerization.
- Elongation: The RNA chain is extended.
- Termination: The RNA chain is released.
Properties of Promoters
- Promoters are typically 40 bp regions on the 5'-side of the transcription start site.
- There are two consensus sequence elements:
- The "-35 region" (TTGACA) which binds the sigma subunit.
- The Pribnow box (TATAAT) located near -10 and ideal for DNA unwinding.
Initiation of Polymerization
- RNA polymerase has two binding sites for NTPs:
- Initiation site: Prefers to bind ATP and GTP (most RNAs begin with a purine at the 5'-end).
- Elongation site: Binds the second incoming NTP.
- The 3'-OH of the first NTP attacks the α-P of the second to form a new phosphodiester bond.
- After making a 6-10 nucleotide oligonucleotide, the sigma subunit dissociates, completing initiation.
- Rifamycin and rifampicin are inhibitors of transcription with different modes of action.
Chain Elongation
- The core polymerase (without the sigma subunit) performs chain elongation.
- Elongation rate is 20-50 bases per second, with slower rates in G/C-rich regions.
- Topoisomerases precede and follow polymerase to relieve supercoiling.
Chain Termination
- There are two main termination mechanisms:
- Rho-dependent termination: The rho termination factor protein is an ATP-dependent helicase that moves along the RNA transcript. It finds the "bubble", unwinds it, and releases the RNA chain.
- Rho-independent termination: Specific sequences in DNA lead to termination.
- The sequence includes an inverted repeat, rich in G:C, which forms a stem-loop structure in the RNA transcript.
- Followed by a run of 6-8 A bases in DNA, which code for Us in the transcript.
Termination Strategies in Bacteria
- Bacteria use a variety of termination strategies.
- Rho-independent termination is the most commonly used method.
- Some genes require Rho for termination.
Transcription in Prokaryotes
- RNA polymerase consists of α, β, β' and ω subunits
- Different subunits have unique roles, with α binding to DNA, β' essential for assembly and activation, and β involved in NTP binding
- Transcription happens in four stages: binding of RNA polymerase, initiation, elongation and termination.
- The accuracy of prokaryotic polymerase is relatively high, with only 1 error in 10,000 bases.
Properties of Promoters
- Promoters are located on the 5'-side of the transcription start site and consist of two key sequences:
- The "-35 region": TTGACA, where the sigma subunit binds
- The Pribnow box: TATAAT, near -10, facilitating DNA unwinding
- Promoters are similar in prokaryotes and eukaryotes, with variations in their sequences and the factors that bind to them.
Initiation of Polymerization
- RNA polymerase has two sites for NTP binding: the initiation site for ATP/GTP and the elongation site for the second NTP.
- The 3'-OH of the first NTP attacks the α-P of the second NTP to form a phosphodiester bond.
- Upon reaching 6-10 nucleotides, the sigma subunit dissociates, marking the completion of initiation.
Chain Elongation
- Elongation is carried out by the core polymerase without the sigma subunit.
- The elongation rate varies and is influenced by G/C content, with faster rates in A/T-rich regions.
- Topoisomerases are involved in relieving supercoiling ahead and behind the polymerase.
Chain Termination
- Two mechanisms are involved:
- Rho-dependent termination, where rho, an ATP-dependent helicase, binds to the transcript, unwinds the DNA, and releases the RNA chain.
- Rho-independent termination involves specific DNA sequences that form a stem-loop structure in the RNA transcript, followed by a string of Us.
Termination Strategies in Bacteria
- Some bacteria use specific, less common mechanisms for transcription termination.
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Description
Explore the key processes involved in transcription in prokaryotes, focusing on the structure and function of RNA polymerase in E. coli. Understand the stages of transcription and the properties of promoters that play critical roles in gene expression.
