Histone modifications

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  • Created by: Ellie0o0o
  • Created on: 27-04-15 16:41
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  • Histone Modifications
    • Covalent histone modifications
      • Phosphorylation
      • Acetylation
        • Lysine residues
          • Free amino group replaced by acyl group
        • Histone becomes netutral
        • Enhances transcription
      • Methylation
        • Most common is 5 methyl-cytosine
        • 5-azacytiolone is an analogous base which cannot be methylated. When added, silent genes become active
        • Mono- di- or tri- methylation
          • Tri- gene silencing
          • Mono- active enhancer
      • Ubiquitination
      • Histone Variants
        • H2A and H3 variants found in DNA
          • Low frequency
        • Have minor differences in amino acid sequences
        • E.g. Histone 3.3 added in transcription coupled process. Helps maintain gene activity
      • Proteins associate
        • Writers
          • Acetyltransferase
        • Readers
          • Bromodomain proteins
            • TFIID
        • Erasers
          • deacetylases
    • Histones have...
      • N-terminal unstructured tail
        • Extends out from the core
        • Subject to covalent modification
        • Flexible due to lack of structure
      • C-terminal histone fold
        • Allows histone dimerization
        • Highly structured
    • Remodelling falls into 2 types
      • Histone Modifying Complexes
        • HATs
          • Histone Acetyl Transferases
            • Acetylation
              • Lysine residues
                • Free amino group replaced by acyl group
              • Histone becomes netutral
              • Enhances transcription
          • e.g. GCN5
        • HDAC
          • Histone deacetylases
            • Repress transcription
      • ATP-dependent remodelling
        • Varies hugely
        • Several complexes use ATP hydrolysis
          • Large with common subunits
          • Fall into 3 groups by ATPase domain
    • Removed for replication, so replication is a "window of opportunity" for change

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