BIOL 2960 Final: SG12 Eukaryotic Gene Expression and Transcription

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Biology And Biomedical Sciences
Biology And Biomedical Sciences BIOL 2960
Kunkel Barbara

I. Eukaryotic vs Prokaryotic Transcription: Eukaryotic Prokaryotic Sigma factors No Yes GTFs Yes No Ground state Off On Multiple Yes No polymerases Nucleus Yes No RNA processing Yes No splicing; no introns Cis-element More varied and different Basic complexity configurations II. Basal transcription in eukaryotes A. Core promoter: set of sequences required to recruit GTFs and RNA polymerase to non- chromatin DNA B. General transcription factors: required for basal transcription; assemble with RNA polymerase to form a pre-initiation complex 1. TFIID/TBP anchors RNA polymerase to DNA 2. TFIIB binds to TFIID, and then RNA polymerase binds to TFIIB. 3. TFIIH is recruited C. DNA binding: RNA Pol II does not bind to the core promoter directly D. C-terminal domain (CTD) phosphorylation and DNA opening 1. CTD: unphosphorylated carboxyl terminal domain of largest subunit is a promoter tether 2. Wraps around DNA and opens it as it is phosphorylated by TFIIH III. Transcriptional regulation in eukaryotes A. Mechanisms that activate transcription 1. Transcription activator proteins a) Promoter or enhancer DNA-binding proteins (1) Nearby promoter elements and enhancer elements harbor binding site for sequence-specific transcriptional activator- repressor proteins, also called transcription regulators (2) b) Co-activators, targets of activation domains, are recruited to the promoter by protein-protein interactions. (1) GTFs (a) TFIID: TBP with TAFs (b) Mediator complex associated with RNAP (2) Histone code writers, especially HATs (3) Chromatin remodelers c) Separable DNA-binding and activation domains: transcription factors often bind to separate upstream sequences although the actual activation sequences are further downstream d) Example: Yeast Gal gene (1) Gal4 protein is a transcription factor that binds to Upstream Activation Sequences (UAS) and helps to recruit GTFs and RNA polymerase. (2) UAS act as enhancers to activate transcription. (3) Gal80 inhibits transcription by binding to Gal4 and preventing UAS from being turned on. (4) Galactose acts as an inducer in this pathway because it binds to Gal3 protein, which when activated, binds to Gal80, preventing it from binding to Gal4. 2. Activation domain interactors a) HAT complex binds to CTD tail and activates chromatin as the polymerase transcribes. b) Nucleo
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