OutlineFigure 13.3cFigure 13.4bFigure 13.4cSlide 5Histone acetylationAcetylation continuedSlide 8Figure 13.29Proposed Mechanism of Histone Deacetylation and Hyperacetylation in Yeast TranscriptionSlide 11Slide 12Slide 13Figure 13.35SummaryOutline•Chromatin modification•Capping•Polyadenylation Welch 2.3082 – 3:15 pmThursdayOct 30.Figure 13.3cFigure 13.4bFigure 13.4cTwo Complexes Play Major RolesHDAC - Histone DeacetylasesHAT - Histone Acetyl TransferaseHistone acetylation•amino groups of lysine side chains•unacetylated histones tend to repress transcription•acetylated histones tend to activate transcription•Histone acetyl transferase (HAT)Histone deacetylaseAcetylation continued•Acetylation of histone tails neutralizes some of the positive charge, causing them to relax their grip on the DNA.•Reduces nucleosome cross-linking. That is; the interaction between histones in neighboring nucleosome. (eg. H4 in one nucleosome and H2A-H2B dimer in the next one.Acetylation continued•Also some TFs recognize acetylated histones. eg. TAFII250 has a double bromodomain and recognizes low level acetylated histones. Once bound it is a HAT and increases acetylation.Figure 13.29Proposed Mechanism of Histone Deacetylation and Hyperacetylation in Yeast TranscriptionPublished by AAAS T. Jenuwein et al., Science 293, 1074 -1080 (2001) Models for euchromatic or heterochromatic histone tail modificationsModels for euchromatic or heterochromatic histone tail modificationsPublished by AAAS T. Jenuwein et al., Science 293, 1074 -1080 (2001) Translating the "histone code."Figure 13.35HATChromatin remodelingBy SWI/SNF complexSummary•Chromatin is a dynamic structure•Histone tails are posttranslationally modified•Different types of modifications constitute “Histone Code”•Different types of modifications are recognized by different proteins to translate the “Histone
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