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Unformatted text preview: TFIIB during preinitiation complex assembly - TFIID binds with or without Gal4p, TFIIB becomes limiting without Gal4p limiting • (b) In order to associate (with (b) Gal4p), TFIIB requires TFIID to be bound in the first step be Weaver 2002 Molecular Biology Ed. 2 Step 1 Step 2 Step 1 Step 2 • specific example of specific transcription factor contributing to assembly of basal apparatus-studies on GAL4 and VP16 GAL4 • GAL4 & VP16 (herpes GAL4 simplex virus protein) are acidic activators acidic that recruit TFIIB that COACTIVATORS COACTIVATORS Lewin Genes VII 2000 Oxford University Press • Transcription factors can contact basal Transcription apparatus indirectly through coactivator coactivator intermediates intermediates • DNA binding and transcriptional activation are in DNA essence encoded by two separate proteins as opposed to one protein with two domains opposed REPRESSORS BLOCK BASAL APPARATUS ASSEMBLY APPARATUS • Transcription activators --> assemble basal Transcription activators assemble transcription apparatus transcription • Transcription repressor --> blocks basal Transcription repressor blocks apparatus assembly apparatus • eg. DR1 repressor prevents TFIIB from joining DR1 TFIID complex --> assembly blocked --> assembly blocked transcription initiation blocked initiation • Eukaryotic repressors block assembly whereas Eukaryotic bacterial or phage repressors interfere with RNAP activity (eg λ repressor or lac repressor) OVERVIEW OF “UPSTREAM” FACTORS OVERVIEW • Upstream transcription factors: flexible activators of Upstream transcription - for instance… transcription • Upstream enhancers: DNA binding sites can be moved Upstream all around a gene all • Transcription factors: DNA binding domains can be Transcription swapped between factors swapped • Conserved mechanism: transcription factor from one Conserved eukaryote functions in distant eukaryotic species (eg. eukaryote yeast GAL4 in Drosophila) Drosophila – Eukaryotic promoter activation - conserved Eukaryotic mechanism and general in nature mechanism – Despite use of general mechanisms, an incredible Despite range of specifities of transcriptional activation can be built up using “mix and match” combinations of upstream factor binding sites in promoter and enhancers enhancers COOPERATIVE ASSEMBLY: TTR TTR PROMOTER IN HEPATOCYTES PROMOTER • Complexity of Complexity eukaryotic gene expression exemplified by TTR TTR transcription transcription • TTR promoter: model for cooperative assembly of basal transcription apparatus in hepatocytes hepatocytes COOPERATIVE ASSEMBLY: TTR TTR PROMOTER IN HEPATOCYTES PROMOTER • Complexity of Complexity eukaryotic gene expression exemplified by TTR...
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