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Nucleosome core particles inhibit DNA triple helix formation
The Biochemical Journal
|October 15, 1996
Summary
DNA triple helix formation is hindered by nucleosome core particles. Triplexes can form only on DNA regions less tightly associated with the protein core, impacting gene targeting strategies.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nucleosomes are fundamental units of DNA packaging in eukaryotes.
- DNA triple helix formation is a strategy for sequence-specific DNA binding.
- Understanding triplex formation within nucleosomes is crucial for gene regulation studies.
Purpose of the Study:
- To investigate the feasibility of forming DNA triple helices on nucleosome core particles.
- To determine the influence of nucleosome structure on triplex-forming oligonucleotide binding.
- To identify conditions that permit or prevent intermolecular DNA triplex formation within nucleosomes.
Main Methods:
- DNase I footprinting was employed to analyze DNA-protein interactions.
- DNA fragments reconstituted with nucleosome core particles were used as targets.
- Both parallel and antiparallel triplex-forming oligonucleotides were tested for binding.
Main Results:
- A 12 bp homopurine target site on a 160 bp DNA fragment within a nucleosome core particle could not be targeted for triplex formation.
- Triplex formation was not enhanced by a triplex-binding ligand.
- Triplexes formed on truncated DNA fragments where the target site was nearer the DNA end, suggesting accessibility is key.
Conclusions:
- Nucleosome core particles significantly impede intermolecular DNA triple helix formation.
- DNA regions with looser association to the protein core are more amenable to triplex formation.
- These findings have implications for the design of targeted gene therapies and molecular tools within chromatin contexts.