ls3-proky-txn-nutshell - Prokaryotic Transcription A...

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STEP1 INITIATION A. Formation of a closed promoter complex RNA polymerase σ factor (subunit) recognizes/binds to CORE PROMOTER special -35 and -10 boxes ( consensus sequences) upstream of the transcription start site If there’s a UP element , it’s recognized by the α - subunit’s C -terminal domain (CTD) o UP elements aren’t essential for transcription initiation, but make the promoter stronger DNA is still in “closed” double strand conformation = loosely associated with RNA polymerase B. Formation of an open promoter complex RNA polymerase melts a short DNA segment around the +1 start site DNA strands are separated and exposed in “open” conformation = tightly associated with RNA pol DNA strands are “bent” Incorporate first few Nucleotides abortive Transcripts C. RNA polymerase forms the first few phosphodiester bonds While still associated with the promoter region (i.e. consensus sequences) May form several abortive transcripts (all the while still associated with DNA; RNA pol never falls off!) sigma cycle
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