Mapping nucleosome positions using DNase-seq.

Area of Science:

• Molecular Biology
• Genomics
• Epigenetics

Background:

• Deoxyribonuclease I (DNase I) was historically used for nucleosome structure studies but is now primarily used for nucleosome-depleted regions in high-throughput sequencing.
• Existing methods for mapping nucleosomes include those requiring genetically modified histones or micrococcal nuclease (MNase) digestion, which primarily targets linker DNA.

Purpose of the Study:

• To develop a novel method for precisely mapping the in vivo translational positions of nucleosomes genome-wide using DNase I.
• To demonstrate the applicability of this DNase I-based approach across different organisms, such as yeast and human.
• To reveal the rotational positioning of nucleosomes and its impact on transcription factor (TF) binding site accessibility.

Main Methods:

• Exploitation of a distinctive DNase I cleavage profile within nucleosome-associated DNA, characterized by a 10.3 base pair oscillation.
• Development of a Bayes-factor-based computational method to accurately map nucleosome positions based on DNase I cleavage patterns.
• Application of the method to generate genome-wide nucleosome maps in yeast and human cell lines.

Main Results:

• The DNase I-based method precisely maps nucleosome translational positions genome-wide, outperforming MNase-based methods in identifying fine-scale positioning details.
• The characteristic DNase I cleavage oscillation reveals nucleosome rotational positioning, providing insights into DNA accessibility.
• Analysis of TF binding sites shows preferential centering on exposed major or minor grooves within nucleosome-associated DNA, suggesting a mechanism for modulating TF interactions.

Conclusions:

• DNase I offers a powerful and versatile tool for high-resolution genome-wide nucleosome mapping, applicable across diverse organisms without genetic modification.
• The method accurately identifies both translational and rotational nucleosome positioning, crucial for understanding genome regulation.
• The findings elucidate how nucleosome structure influences TF binding, providing a deeper understanding of gene regulation dynamics.