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Messenger RNA interferase RelE controls relBE transcription by conditional cooperativity
Martin Overgaard1, Jonas Borch, Mikkel G Jørgensen
1Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
Molecular Microbiology
|June 6, 2008
Summary
Prokaryotic toxin-antitoxin (TA) systems use antitoxins to neutralize toxins. The RelE toxin in E. coli controls relBE transcription through conditional cooperativity, acting as both a repressor and derepressor.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Prokaryotic toxin-antitoxin (TA) loci are genetic elements encoding stable toxins and unstable antitoxins.
- Antitoxins neutralize cognate toxins via complex formation and autoregulate TA operon transcription.
- Toxins typically act as co-repressors, but can also stimulate transcription.
Purpose of the Study:
- To analyze the mechanistic aspects of how the RelE toxin from Escherichia coli functions as both a co-repressor and derepressor of relBE transcription.
- To elucidate the role of toxin-antitoxin stoichiometry in regulating TA operon transcription.
Main Methods:
- Analysis of RelE and RelB protein interactions and binding to operator sites.
- Mutational analysis of operator sites within the relBE promoter region.
- Investigating the effects of varying RelE and RelB concentrations on transcription.
Main Results:
- When RelB was in excess, trimeric RelB(2)*RelE complexes bound cooperatively to operator sites, repressing transcription.
- When RelE was in excess, it stimulated relBE transcription by releasing the RelB(2)*RelE complex from operator DNA.
- Mutational analysis revealed that excess RelE counteracted cooperative binding of the complexes to operator sites.
Conclusions:
- RelE controls relBE transcription through a mechanism of conditional cooperativity, dependent on the relative concentrations of RelE and RelB.
- The stoichiometry of toxin and antitoxin dictates the regulatory outcome of TA operon transcription.
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