Active and passive repression

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  • Transcriptional Repression
    • Chromatin + nucleosomes are repressors. Therefore activators are required at all promoters (even in euch areas)
      • Relief can come from chromatin remodelling / modifying
      • Gene-specific repression is needed to ensure gene is OFF till needs to be transcribed
        • E.g. activator A turns on 100 genes, you only want 90 - use repressor to block activation of 10
    • Passive repression
      • Steric hindrance
        • Competitive binding with activator
      • Masking / quenching
        • Interaction with activation domain
      • Interacting with GTF
        • Binding to GTF so that activator can't interact with it
      • Sequestering activator in cytoplasm
        • Isolate activator by repressor holding onto it until signal for release
    • Active repression
      • HDACs
        • E.g. Sin3 + NURD
      • Formation of facultative heterochromatin
        • Long range repression
      • Histone methyltransferases
        • Methylated histones can bind silencing proteins
        • E.g. HP1
          • Directs formation and spread of heterochromatin
        • E.g. SUV39H1


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