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Lecture

Lecture 23 - Transcription Initiation - BIOL308.pdf

5 Pages
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Department
Biology
Course Code
BIOL 308
Professor
Bruce Wolff

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Lecture 23Transcription Initiation by RNAP IITranscription is highly regulatedOne gene could be transcribed in response tomultiple conditionsEg Heat shock protein s important for cell protection are expressed when cells are exposed to high temperature and heavy metalsDifferent conditions are associated with different cis elementswhich bind different regulatory proteinstranscription factorsGene that responds to multiple conditionshas multiple cis elements4 in gene A 3 in gene BEg There are a heat shock response element HRE and metal responsive element MRE in promoter regions of genes for heat shock proteinsCertain signalcondition could increase andor decrease transcription of different genesDifferent genes which respond to the same signal in the same way all have the same cis elementOrange element 3 in promoters of genes A and BThere is no consistent location of cis elements among different genesOrange element 3 in different locations relative to genes A and BIn vitro experiments cis elements responding to different signals are cloned upstream from a reporter geneCause the reporter gene to be transcribed when particular signal is appliedPromotersare modularmix and matchVariety of elements can contribute to promoter function bind RNAP IINone is essential for or common to all promotersIn any individual promoter elements may differ in number location orientationSummary of modular nature of RNAP II promotersMany have a TATA boxas a core elementMajority of those that dont have initiator sequence or GCislandsinsteadProximal elementrequired for developmental environmental tissuespecific etc expressionPromoters that respond to same conditionsbut control expression of different genes havesame cis elementsalthough they may not be located in the same position relative to the start site of transcriptionEnhancersometimes composed of multiple binding sitesfor different regulatory proteins the combination of trans factorsleads to increased transcription initiationOutcomeexpression of one genecan be induced or increased or decreased or shutoff underin different conditions due to the modularityof genes promoterRNA polymerase IIRecall RNAP II catalyzes transcription of mRNAs and some small nuclear RNAs snRNAsRecall e coli core RNAP cannot initiate transcription withoutsigma subunitand functions as an initiation factorEukaryotic RNAP holoenzyme cannot bind to DNA in absence of specific transcription initiation factors general transcription factorsGeneral Transcription FactorsPosition RNAP II at transcription initiation sites bend DNA promote tight binding prevent nucleosome reformationRequired by transcription of most genes that are transcribed by RNAPIItranscriptioninitiation complex RNAP IIGFP Bound in general transcription factors bound to promoter regionTFIIA TFIIB TFIID TFIIE TFIIF and TFIIHStands for transcription factor RNAP II Aetc NOTES FROM LECTURES Page 1
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