Stretching DNA to quantify nonspecific protein binding.

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Nonspecific protein-DNA interactions are crucial for biological processes.
• The lambda repressor protein (CI) is essential for maintaining lysogeny in E. coli.
• CI specifically binds to viral DNA to form a repressive loop.

Purpose of the Study:

• To investigate the role of nonspecific DNA binding by the lambda repressor protein (CI).
• To quantify the dissociation constant for nonspecific CI-DNA binding.
• To measure the DNA compaction induced by CI binding.

Main Methods:

• Utilized a partition function-based approach to analyze DNA extension measurements.
• Performed multiple cycles of DNA extension and relaxation at varying CI concentrations.
• Employed single-molecule imaging and thermodynamic/kinetic measurements.

Main Results:

• Quantified the dissociation constant for nonspecific CI-DNA binding at approximately 100 nM.
• Measured an induced DNA compaction of about 10% due to CI binding.
• Demonstrated that nonspecific binding plays a significant role in CI's function.

Conclusions:

• Nonspecific DNA binding by CI is a key mechanism for maintaining lysogeny.
• The developed phenomenological approach accurately measures protein-DNA interactions.
• Nonspecific binding contributes to the stability of the lysogenic state.