Asymmetrical nucleosomal DNA signatures regulate transcriptional directionality

Area of Science:

• Molecular Biology
• Genetics
• Epigenetics

Background:

• In vitro studies suggest DNA orientation around nucleosomes affects transcription efficiency.
• The in vivo relevance and regulatory role of this nucleosomal DNA asymmetry in transcriptional directionality remain unclear.

Purpose of the Study:

• To investigate whether functional asymmetry exists in vivo within nucleosomes.
• To determine if this asymmetry regulates transcriptional directionality.

Main Methods:

• Analysis of nucleosome stability and DNA accessibility in vivo.
• Assessing the impact of DNA sequence orientation on transcription.
• Utilizing Micrococcal Nuclease (MNase) accessibility assays.

Main Results:

• Proximal and distal DNA segments of nucleosomes contribute differentially to genome-wide nucleosome stability.
• In +1 nucleosomes, DNA orientation dictates whether transcription is facilitated or hindered, linked to asymmetrical DNA-histone interactions.
• A specific DNA signature in +1 nucleosomes confers asymmetric accessibility and inverts sense/antisense transcription balance when transferred to downstream nucleosomes.

Conclusions:

• Nucleosomal DNA possesses inherent asymmetrical properties that actively modulate transcriptional directionality in vivo.
• This DNA-encoded asymmetry provides a mechanism for regulating gene expression directionality at the nucleosome level.