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Gal4p zn binding transcription factor but not gal4p

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Unformatted text preview: VII 2000 Oxford University Press • Transcription factors: often one DNA binding domain Transcription & one activating domain contacting basal apparatus one • eg. Gal4p - Zn binding transcription factor (but not Gal4p Zn not Zn-finger transcription factor) contains separable Zn DNA binding & transcription activation domains DNA Gal4p TRANSCRIPTION FACTOR: MODULAR DOMAINS MODULAR Lewin Genes VII 2000 Oxford University Press • Gal4p: binds to DNA at UAS; activates transcription; & Gal4p: binds Gal80p regulatory protein binds • When galactose levels low, Gal80p blocks Gal4p When transcriptional activation transcriptional • Gal4p activation domain attached to another DNA Gal4p binding domain still activates transcription - ie. Gal4p ie Gal4p DNA binding and activation domains are separable Gal4p ACTIVATION DOMAIN INDEPENDENT OF BINDING SPECIFICITY OF Activated by Activated endogenous Gal4p endogenous Weaver 2002 Molecular Biology Ed. 2 • Gal4p activation domain joined to LexA DNA binding Gal4p domain activates gene expression from LexA binding site (LexA operator) (remember LexA is a bacterial repressor) (LexA • Gal4p modular transcription factor: if Gal4p in vicinity of Gal4p promoter, regardless of how it got there, it activates transcription (doesn’t “care” about how it binds DNA) transcription HIV tat ACTIVATION REQUIRES NONHIV SPECIFIC TETHERING Lewin Genes VII 2000 Oxford University Press • HIV tat stimulates HIV transcription without even binding DNA - tat binds tar mRNA & tar while attached, tat activation domain acts at promoter acts • If tat RNA binding If domain exchanged with DNA binding domain, tat still works as activator works UPSTREAM TRANSCRIPTION FACTORS: INTERACTIONS WITH BASAL APPARATUS INTERACTIONS Lewin Genes VII 2000 Oxford University Press • Eukaryotic transcription factors do not directly contact RNA Eukaryotic polymerase (unlike prokaryotes and phage) polymerase • Although not generally called a transcription factor, CAP-cAMP Although activates transcription by direct interaction with RNA pol activates • Activation domains of eukaryotic transcription factors interact with Activation basal apparatus through contact with general (TFIIX) factors - often TFIID, TFIIB, or TFIIA which are involved in relatively early stages of TFIID TFIIB, assembly assembly UPSTREAM TRANSCRIPTION FACTORS: INTERACTIONS WITH BASAL APPARATUS INTERACTIONS Lewin Genes VII 2000 Oxford University Press • given that contact is made with basal apparatus during assembly, it given is likely that upstream transcription factors enhance transcription by increasing a rate-limiting step of basal apparatus formation rather than influencing its activity than • TFIID most common target f...
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