8 Questions
Which subunit of the E. coli RNA polymerase holoenzyme is responsible for the initiation of transcription?
σ
What is the primary function of the β' subunit in E. coli RNA polymerase?
DNA template binding region
Which region of the promoter in E. coli is also known as the Pribnow box?
-10 sequence
How long must a promoter be in E. coli to avoid occurrence by chance?
12 bp
What happens to the sigma factor during the transcription process in E. coli?
It is released after promoter clearance
Which protein binds to the RNA polymerase after the sigma factor is released during transcription in E. coli?
Nus A protein
What are Rho-independent terminators characterized by?
Hairpin forming sequences
Which term describes the bases preceding the initiation site in transcription?
Upstream sequences
Study Notes
E.Coli RNA Polymerase
- Consists of core enzyme (α β β' ω) and holoenzyme (α2 β β' ωσ)
- Functions of subunits: • α: assembles tetrameric core • β: ribonucleoside triphosphate binding site • β': DNA template binding region • σ: initiates transcription
Promoters
- Must be >12 bp to avoid occurrence by chance
- Have small conservation in sequence
- Comprise four main regions: • Startpoint • -10 sequence (Pribnow box) • -35 sequence • 17 nucl spacer sequence between -10 and -35 sequences
Transcription Unit Numbering
- Transcript initiation site is +1
- Bases preceding initiation site have minus (−) prefixes and are referred to as upstream sequences
- Bases following initiation site have plus (+) prefixes and are referred to as downstream sequences
Transcription Initiation
- RNA polymerase holoenzyme binds to promoter region in DNA
- Localized unwinding of both DNA strands occurs around -10 region
- Phosphodiester bonds form between first few ribonucleotides in nascent RNA chain
- Conformational change in enzyme, promoter is cleared
- Sigma Factor is released, replaced by Nus A protein to form antitermination complex
Transcription Termination
- RNA polymerase transcribes until it meets a terminator
- Transcription stops, RNA product dissociates from DNA template
- Two types of terminators in E. coli: • Rho-dependent terminators: require protein factor (ρ) • Rho-independent terminators: do not require ρ
This quiz covers the structure and function of E. Coli RNA Polymerase subunits and the characteristics of promoters in transcription.
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