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What is part I of the histone code hypnothesis?
Histone modifications can have remote effects on other histones.
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What are the two types of Repression?
- Histone Stabillizing
- Nucleosome Blocking
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Describe Repression by Nucleosome Blocking.
- A Nucleosome sits atop the promotor region, blocking transcription.
- Only after removal of the Nucleosome can transcription occur.
- An activator is required to remove the nucleosome and promote transcription.
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Describe Histone Stabillized Repression.
- Histones and Nucleosomes are bound to the DNA but on the promotor.
- Transcription does not occur because Histone H1 stabillizes the Nucleosomes flanking the promotor.
- Removal of Histone H1 (Nucleosomes remain) gives "Competant" transcription.
- Binding of an Activator gives "Active" transcription.
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Which is removed first, Histones or Nucleosomes?
Histones, then Nucleosomes.
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What Histone does Histone repression use?
Histone H1
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What is Chromatin Remodelling?
Selectively altering chromatin at defined locations.
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What are the two types of Chromatin Remodelling?
- Nucleosome Displacement (Removal)
- Nucleosome Repositioning (Octamer Sliding)
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How does the Swi/SNF complex work?
- Binds with BRG-1
- Uses ATP to "loosen" chromatin structure
- Binds to Octamer
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What does Swi/SNF do?
Converts a Silent Gene to an Active Gene
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What is the Chromatin Remodelling complex?
Swi/SNF
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What is the Second Part of the Histone Code Hypothesis?
Different Modifications are read differently, allowing for complex regulation of Structure and Transcription.
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Can Nucleosomes be present at sites of high Transcription?
Yes.
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How does elongation deal with Nucleosomes?
The FACT complex (associated with polymerase) remodels DNA ahead and behind the active site.
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What does FACT stand for?
Facilitates Chromatin Transcription
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