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Histone deacetylation by Sir2 generates a transcriptionally repressed nucleoprotein complex
Xuejun Huang Parsons1, Sandra N Garcia, Lorraine Pillus
1Section of Molecular Biology, 0347, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0347, USA.
Summary
Sir2 (silent information regulator 2) is an NAD-dependent histone deacetylase. This study shows dSir2 represses transcription only with hyperacetylated histones, forming a repressive chromatin structure.
Area of Science:
- Biochemistry
- Molecular Biology
- Epigenetics
Background:
- Sir2 is an NAD-dependent histone deacetylase crucial for transcriptional silencing.
- Understanding the precise mechanism of Sir2 function is essential for comprehending gene regulation.
Purpose of the Study:
- To investigate the biochemical properties and mechanism of action of purified recombinant Drosophila Sir2 (dSir2).
- To determine the conditions under which dSir2 mediates transcriptional repression.
Main Methods:
- Histone deacetylation assays using purified recombinant dSir2.
- In vitro transcription experiments with naked DNA, native chromatin, and hyperacetylated histone-DNA complexes.
- Analysis of histone-DNA complex formation and nuclease resistance.
- Comparison with Drosophila HDAC1 and yeast Sir2.
Main Results:
- dSir2 deacetylates a broad range of acetylated lysine residues.
- dSir2 represses transcription (50- to 100-fold) specifically with hyperacetylated histones in an NAD-dependent manner.
- dSir2 mediates the formation of a nuclease-resistant histone-DNA complex.
- Transcriptional repression by dSir2 correlates with deacetylation activity.
Conclusions:
- Sir2-mediated transcriptional repression is dependent on the acetylation state of histones.
- Deacetylation by Sir2 induces a conformational change in histones, leading to a transcriptionally repressive chromatin structure.