DNA Can Unwrap

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DNA Can Unwrap
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Nucleosome Remodeling Complexes

• Switch/Sniff complex (SWI/SNF)
• Imitation Switch (ISWI)
• Mi2/NuRD (Nucleosome Remodeling and histone
  Deacetylation

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Nucleosome Remodeling
Restructure
Alter position of nucleosome
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As RNA polymerase advances, DNA
unspools Nucleosome is handed off to stretch of
DNA behind the advancing polymerase
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Nucleosome-Free Zones

• Found within regulatory regions of genes
• Required for the assembly of the transcriptional
  machinery
• Histones compete with other DNA binding
  proteins, such as transcriptional activators

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Formation of Nucleosome-Free Zones
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Nucleosome Positioning
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Nucleosome Positioning
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N-terminal Histone Modifications

• Lys residues acetylated
• methylated
• Ser residues phosphorylated

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Acetyl-Lysine
Transcriptionally Repressed
Transcriptionally Active
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The Histone Code
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Bromo and Chromo Domains

• Domains found in histone-binding proteins
• Bromo domain binds
• acetylated lysines

• Chromo domain binds methylated lysines

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Ac and Me Modifications Recruit Proteins to the
Nucleosome
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Inheritance of Histones After Replication
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Histone Chaperones