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Visualization of trp repressor and its complexes with DNA by atomic force microscopy
E Margeat1, C Le Grimellec, C A Royer
1Centre de Biochimie Structurale, INSERM U 414-CNRS UMR 9955-Université Montpellier I, Montpellier, France.
Biophysical Journal
|November 25, 1998
Summary
The trp repressor (TR) uses protein-protein interactions to regulate transcription. Higher TR concentrations decrease DNA-binding specificity, leading to protein assembly formation.
Area of Science:
- Molecular Biology
- Biophysics
- Genetics
Background:
- Transcriptional regulation is a fundamental biological process.
- The trp repressor (TR) is a key regulator of the tryptophan operon.
- Understanding TR's regulatory mechanisms requires visualizing its interactions.
Purpose of the Study:
- To visualize protein/protein and protein/DNA complexes of the trp repressor (TR).
- To investigate the role of TR concentration and L-tryptophan in DNA binding specificity.
- To elucidate the contribution of protein-protein interactions to TR-mediated transcriptional regulation.
Main Methods:
- Tapping mode atomic force microscopy (AFM) was employed.
- Plasmid fragments with specific (trp EDCBA, trp R) and nonspecific DNA sequences were used.
- Varying concentrations of TR (1-5 nM) with and without L-tryptophan were analyzed.
Main Results:
- Specific and nonspecific TR-DNA complexes, along with free TR assemblies, were visualized in the presence of L-tryptophan.
- Increasing TR concentration reduced DNA-binding specificity.
- Formation of large TR protein assemblies correlated with decreased specificity, suggesting oligomerization.
Conclusions:
- Protein-protein interactions play a significant role in transcriptional regulation by the trp repressor.
- TR oligomerization influences its DNA-binding specificity.
- The presence or absence of the co-repressor (L-tryptophan) affects TR complex formation and visualization.