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Percolation of the phd repressor-operator interface.
Xueyan Zhao1, Roy David Magnuson
1Department of Biological Sciences, University of Alabama, Huntsville, AL 35758, USA.
Journal of Bacteriology
|March 4, 2005
Summary
The Phd repressor-antitoxin protein and its operator-binding sites coevolved to alter specificity while maintaining function. This evolution in toxin-antitoxin systems may be common, facilitating bacterial speciation.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Toxin-antitoxin systems, like the P1 plasmid addiction operon, regulate gene expression through autoregulation.
- The Phd repressor-antitoxin protein binds to specific DNA sites to control transcription, with the Doc toxin enhancing this repression.
Purpose of the Study:
- To investigate a homologous toxin-antitoxin operon in Salmonella enterica serovar Typhimurium.
- To understand the molecular basis for altered repressor-operator specificity in this homologous system.
Main Methods:
- Comparative analysis of the Salmonella Typhimurium operon with the P1 plasmid operon.
- Identification of key amino acid and DNA sequence variations responsible for specificity differences.
Main Results:
- A homologous operon in Salmonella Typhimurium exhibits similar autoregulation but altered repressor-operator specificity.
- Specificity differences map to the seventh amino acid of the repressor and specific positions in the DNA-binding sites.
- The seventh amino acid in homologous repressors is highly variable, suggesting frequent evolutionary changes in specificity.
Conclusions:
- The repressor-operator interface coevolved to retain interaction while altering specificity, driven by negative feedback, flexible binding, and gene duplication.
- These mechanisms facilitate the evolution of toxin-antitoxin systems, potentially contributing to bacterial speciation.