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RecA-dependent cleavage of LexA dimers
Kim C Giese1, Christine B Michalowski, John W Little
1Department of Biochemistry and Molecular Biophysics, University of Arizona, 1007 E. Lowell Street, Tucson, AZ 85721, USA.
Journal of Molecular Biology
|February 1, 2008
Summary
LexA dimers are cleavable in Escherichia coli's SOS response, with RecA acting as a co-protease. RecA likely allosterically stimulates LexA cleavage by promoting a conformational change.
Area of Science:
- Molecular Biology
- Bacterial Genetics
- DNA Repair Mechanisms
Background:
- The SOS response in Escherichia coli is a critical DNA damage repair mechanism.
- LexA repressor controls the SOS response by inhibiting gene expression.
- RecA protein, activated by DNA damage, acts as a co-protease to cleave LexA.
Purpose of the Study:
- To reexamine the proteolytic cleavage of the LexA repressor in Escherichia coli.
- To investigate the role of LexA dimerization in RecA-dependent cleavage.
- To elucidate the mechanism by which RecA stimulates LexA cleavage.
Main Methods:
- Biochemical assays to study LexA cleavage kinetics.
- Analysis of LexA dimerization state under various conditions.
- Investigating the influence of LexA subunit interactions on cleavage rates.
Main Results:
- RecA-dependent cleavage of LexA is efficient even when LexA exists primarily as dimers.
- LexA dimers exhibit slow dissociation rates.
- Interactions within LexA dimers appear to modulate cleavage rates.
- RecA promotes the transition of LexA to a cleavable conformation, suggesting an allosteric mechanism.
Conclusions:
- LexA dimers are the functional units cleaved during the SOS response.
- RecA's co-protease activity involves an allosteric modulation of LexA's conformation.
- Understanding LexA cleavage provides insights into bacterial DNA repair regulation.
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