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Updated: Jun 6, 2026
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Chromatin Immunoprecipitation (ChIP) to Assay Dynamic Histone Modification in Activated Gene Expression in Human Cells
Published on: July 30, 2010
Silenced chromatin is permissive to activator binding and PIC recruitment
1Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA.
Cell
|May 12, 2001
Summary
Repressive heterochromatin permits transcription factor binding but blocks gene activation. Yeast studies show silencing proteins do not prevent preinitiation complex assembly but inhibit downstream steps without altering histone acetylation.
Area of Science:
- Molecular Biology
- Epigenetics
- Gene Regulation
Background:
- Chromatin structure is traditionally viewed as a barrier to DNA accessibility for transcription factors.
- The role of heterochromatin in regulating gene expression is complex and not fully understood.
Purpose of the Study:
- To investigate how SIR-generated heterochromatin affects transcription factor and preinitiation complex binding in yeast.
- To determine the mechanism by which heterochromatin represses transcription.
Main Methods:
- Utilized a yeast heat shock gene model system flanked by mating-type silencers.
- Analyzed the occupancy of transcription factors (HSF) and preinitiation complex components (TBP, Pol II) on heterochromatic promoters.
- Examined histone modifications and displacement during heterochromatin activation.
Main Results:
- Repressive heterochromatin allows constitutive binding of HSF, TBP, and Pol II to the promoter.
- These factors coexist with silencing proteins and deacetylated histones.
- Heterochromatic promoters are occupied by TBP and Pol II, indicating a downstream blockage of transcription.
Conclusions:
- SIR-mediated heterochromatin represses transcription downstream of preinitiation complex recruitment, not by restricting DNA access.
- Heterochromatin activation can occur without histone displacement or changes in acetylation state.
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