DNA triple-helix formation on nucleosome-bound poly(dA).poly(dT) tracts

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Nucleosomes are the fundamental units of DNA packaging in eukaryotes.
• DNA triple helices are non-B DNA structures with potential roles in gene regulation.
• Understanding DNA structure and interactions within nucleosomes is crucial for comprehending genome function.

Purpose of the Study:

• To investigate the feasibility of forming intermolecular DNA triple helices on nucleosome-bound DNA fragments.
• To determine how the stability of these triple helices is influenced by the DNA sequence and its orientation relative to the nucleosome.
• To assess the structural consequences of triplex formation on the DNA-nucleosome interaction.

Main Methods:

• DNase I footprinting to probe DNA accessibility.
• Hydroxyl-radical footprinting to map DNA-protein contacts.
• Biophysical techniques to assess triplex stability.

Main Results:

• Intermolecular DNA triple helices can form on nucleosome-bound DNA containing A.Tn tracts.
• Triplex stability is dependent on the orientation of the A tract relative to the nucleosome's protein surface.
• While DNA remains associated with the nucleosome, the characteristic phased cleavage pattern is disrupted near the triplex, indicating local DNA repositioning.

Conclusions:

• Nucleosome-bound DNA can accommodate intermolecular triple helix formation.
• The structural plasticity of nucleosomal DNA allows for local rearrangements upon triplex formation.
• These findings provide insights into the dynamic interplay between DNA structure, protein binding, and chromatin organization.