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Updated: Jun 6, 2026

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.
Abstract:
Chromatin is thought to repress transcription by limiting access of the DNA to transcription factors. Using a yeast heat shock gene flanked by mating-type silencers as a model system, we find that repressive, SIR-generated heterochromatin is permissive to the constitutive binding of an activator, HSF, and two components of the preinitiation complex (PIC), TBP and Pol II. These factors cohabitate the promoter with Sir silencing proteins and deacetylated nucleosomal histones. The heterochromatic HMRa1 promoter is also occupied by TBP and Pol II, suggesting that SIR regulates gene expression not by restricting factor access to DNA but rather by blocking a step downstream of PIC recruitment. Interestingly, activation of silent promoter chromatin occurs in the absence of histone displacement and without change in histone acetylation state.
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