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DNA sequence-dependent mechanics and protein-assisted bending in repressor-mediated loop formation
James Q Boedicker1, Hernan G Garcia, Stephanie Johnson
1Departments of Applied Physics and Biology, California Institute of Technology, 1200 California Boulevard, Pasadena, CA 91125, USA.
Physical Biology
|November 16, 2013
Summary
DNA sequence flexibility does not impact gene regulation in bacterial transcription factor-mediated looping. DNA-bending protein HU masks intrinsic sequence-dependent DNA mechanics, revealing a dominant role for protein-induced bending in gene regulation.
Area of Science:
- Molecular Biology
- Biophysics
- Genetics
Background:
- DNA mechanical properties, including sequence-dependent flexibility, influence gene regulation.
- The role of DNA sequence in transcription factor-mediated looping remains poorly understood.
- DNA mechanics are crucial for processes like nucleosome positioning and gene expression.
Purpose of the Study:
- To investigate the influence of sequence-dependent DNA flexibility on bacterial transcription factor-mediated looping.
- To quantify the relative contributions of DNA sequence and protein HU to DNA mechanical properties in looping.
- To determine if intrinsic DNA flexibility affects in vivo gene regulation.
Main Methods:
- Utilized synthetic DNA constructs with known sequence variations and the Lac repressor system.
- Employed in vitro single-molecule assays and in vivo transcription assays to measure DNA looping and gene regulation.
- Applied statistical mechanics to predict and analyze DNA loop formation influenced by sequence and protein binding.
Main Results:
- Surprisingly, sequence-dependent DNA flexibility did not significantly affect in vivo gene regulation in the studied system.
- The DNA-bending protein HU was found to dominate DNA mechanics, masking the intrinsic sequence-dependent flexibility.
- Experimental and theoretical analyses quantified the interplay between protein-induced bending and intrinsic DNA properties.
Conclusions:
- Protein-induced DNA bending, specifically by HU, plays a more critical role in regulating gene expression than intrinsic DNA sequence flexibility.
- Understanding the mechanical contributions of proteins is essential for a predictive model of gene regulation.
- This study provides a quantitative framework for analyzing DNA mechanics in genome regulation.
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