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Analysis of the sequence-specific interactions between Cro repressor and operator DNA by systematic base substitution
Y Takeda1, A Sarai, V M Rivera
1Laboratory of Mathematical Biology, National Cancer Institute-Frederick Cancer Research Facility, MD 21701.
Summary
Researchers quantified Cro repressor binding affinities to DNA operators, revealing additive free energy changes for base substitutions. This allows prediction of repressor-operator interactions and refines models of sequence-specific DNA binding.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Cro repressor is a key protein in bacteriophage lambda genetic regulation.
- Understanding Cro repressor-operator DNA interactions is crucial for gene expression control.
- Existing models for Cro repressor binding sites require experimental validation.
Purpose of the Study:
- To quantitatively measure the binding affinities of Cro repressor to wild-type and mutant OR1 operator DNA sequences.
- To determine the contribution of individual base pairs to Cro repressor binding specificity.
- To refine and challenge existing models of Cro repressor-operator DNA recognition.
Main Methods:
- Chemically synthesized wild-type and mutant OR1 operator DNA sequences.
- Quantitative measurement of Cro repressor binding affinities using purified protein.
- Site-directed mutagenesis to generate cro mutants and analyze their DNA binding properties.
Main Results:
- Cro repressor binding affinities were measured for all possible base-pair substitutions in the OR1 operator.
- Sequence-specific interactions occur at specific positions within the operator, with near-symmetrical binding.
- Binding free energy changes are largely additive, enabling prediction of binding affinities based on single base substitutions.
- Analysis of cro mutants revealed sequence-specific contacts differing from previously proposed models.
Conclusions:
- Cro repressor binding to operator DNA is governed by additive free energy contributions from base substitutions.
- The binding site interactions are primarily located at specific outer and central positions of the operator.
- The study provides a refined understanding of Cro repressor-DNA recognition, challenging existing structural models.