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Binding characteristics of Escherichia coli biotin repressor-operator complex
K C Lin1, A Campbell, D Shiuan
1Molecular Biology Division, Development Center for Biotechnology, Taipei Taiwan, R.O.C.
Biochimica Et Biophysica Acta
|November 11, 1991
Summary
This study investigates the biotin repressor (BirA) and its DNA binding. We found that two BirA monomers likely bind to the biotin operator, influencing gene transcription.
Area of Science:
- Molecular Biology
- Gene Regulation
- Biochemistry
Background:
- The biotin operon (bioA-BFCD) exhibits divergent transcription from a shared regulatory region.
- Biotin repressor (BirA) and biotinyl-5'-adenylate co-repress transcription.
- The multimeric state and DNA-binding mechanism of BirA remain incompletely understood.
Purpose of the Study:
- To characterize the DNA binding properties of the biotin repressor (BirA).
- To determine the stoichiometry of the BirA-operator complex.
- To elucidate how BirA binding affects transcription.
Main Methods:
- Isolation of BirA protein from a recombinant overproducing strain.
- Restriction enzyme site protection assays to map operator length.
- Mobility shift assays to analyze repressor-operator interactions.
- Direct measurement of repressor-operator complex stoichiometry.
Main Results:
- Restriction enzyme protection suggests the biotin operator is approximately 40 bp long.
- A single DNA band in mobility shift assays indicates a potential single-step binding reaction.
- Stoichiometry determination reveals that two BirA monomers bind to the wild-type or half-palindromic biotin operator.
Conclusions:
- The biotin repressor (BirA) likely functions as a dimer or tetramer in binding DNA.
- Two BirA monomers occupy the biotin operator, contributing to transcriptional co-repression.
- This binding stoichiometry provides insights into the regulation of the biotin operon.