E. Coli RNA Polymerase and Promoters

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.