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lac repressor mutants with double or triple exchanges in the recognition helix bind specifically to lac operator
J Sartorius1, N Lehming, B Kisters
1Institut für Genetik der Universität zu Köln, FRG.
The EMBO Journal
|April 1, 1989
Summary
Researchers engineered lac repressor mutants to significantly repress beta-galactosidase synthesis. These mutants exhibit specific binding to altered lac operator DNA sequences, advancing our understanding of protein-DNA interactions.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The lac repressor protein controls the expression of genes involved in lactose metabolism in Escherichia coli.
- Understanding the precise interactions between the lac repressor and its operator DNA is crucial for gene regulation studies.
Purpose of the Study:
- To isolate and characterize lac repressor mutants with enhanced DNA-binding affinity and specificity.
- To investigate the structural basis of lac repressor-operator recognition.
Main Methods:
- Isolation and characterization of lac repressor mutants.
- Assaying beta-galactosidase synthesis levels in Escherichia coli.
- Mapping mutations to specific residues within the lac repressor's recognition helix.
Main Results:
- Several lac repressor mutants were identified, capable of repressing beta-galactosidase synthesis up to 200-fold.
- Mutations were localized to residues 1, 2, and 6 of the recognition helix, which interact with specific base pairs of the lac operator.
- A mutant protein with combined mutations (residues 1, 2, and 6) demonstrated specific binding to a lac operator variant with three symmetric base pair exchanges.
Conclusions:
- Specific amino acid residues in the lac repressor's recognition helix are critical for operator binding specificity.
- Engineering these residues can create novel repressor variants with altered DNA-binding properties.
- This work provides insights into the molecular mechanisms of sequence-specific protein-DNA recognition.