Lecture 10 chapter 11&12 MB - Class I Factors The...

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Class I Factors The preinitiation complex at rRNA promoters much simpler than that of class II preinitiation complexes RNA polymerase I A core-binding factor, SL1 (human) or TIF-IB A UPE-binding factor: upstream-binding factor (mammalian UBF) or upstream activating factor (yeast UAF) 11-1
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The Core-Binding Factor The core-binding factor Human SL1 originally isolated on the basis of its ability to direct polymerase initiation SL1 also shows species specificity The fundamental transcription factor required to recruit RNA polymerase I 11-2
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Upstream-Binding Factor (UBF) UBF is an assembly factor that helps the core- binding factor to bind to the core promoter element Severely bends the DNA as an architectural transcription factor Human UBF Stimulates transcription by polymerase I Can activate the intact promoter, or the core element alone mediates activation by the upstream promoter element (UPE) Degree of reliance on UBF varies considerably from one organism to another 11-3
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Structure and Function of SL1 Human core-binding protein SL1 is composed of TBP and three TAFs (TAF I 110, TAF I 63, TAF I 48) which bind TBP tightly SL1 TAF I s are not the same as TFIID TAFs Yeast and other organisms have core-binding protein TAF I s that are different from those in humans 11-4
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SL1 alone does not footprint but is necessary for transcription – consists of tree TAF’s bound to TBP Extends UBF footprint in core and UPE regions Increases DNAse I digestion in select locations UBF can stimulate transcription without UPE binding
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Class III Factors TFIIIA transcription factor binds the internal promoter of the 5S rRNA gene and stimulates its transcription Two other transcription factors TFIIIB and TFIIIC Transcription of all classical class III genes (e.g. tRNA) requires TFIIIB and TFIIIC but not TFIIIA Transcription of 5S rRNA genes requires all three 11-6
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TFIIIA TFIIIA was the first eukaryotic transcription factor to be discovered First zinc finger type DNA-binding protein described “finger-shaped” protein domain that contains 4 amino acids that bind a zinc ion Nine zinc fingers insert into the major groove on either side of the promoter for the 5S rRNA gene 11-7
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TFIIIB and TFIIIC Both required for transcription of classical polymerase III genes Dependent on each other for their activities TFIIIC (assembly factor) binds both
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