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Updated: May 5, 2026
Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System
Published on: August 21, 2016
A bacterial toxin inhibits DNA replication elongation through a direct interaction with the β sliding clamp
Christopher D Aakre1, Tuyen N Phung1, David Huang2
1Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Abstract:
Toxin-antitoxin (TA) systems are ubiquitous on bacterial chromosomes, yet the mechanisms regulating their activity and the molecular targets of toxins remain incompletely defined. Here, we identify SocAB, an atypical TA system in Caulobacter crescentus. Unlike canonical TA systems, the toxin SocB is unstable and constitutively degraded by the protease ClpXP; this degradation requires the antitoxin, SocA, as a proteolytic adaptor. We find that the toxin, SocB, blocks replication elongation through an interaction with the sliding clamp, driving replication fork collapse. Mutations that suppress SocB toxicity map to either the hydrophobic cleft on the clamp that binds DNA polymerase III or a clamp-binding motif in SocB. Our findings suggest that SocB disrupts replication by outcompeting other clamp-binding proteins. Collectively, our results expand the diversity of mechanisms employed by TA systems to regulate toxin activity and inhibit bacterial growth, and they suggest that inhibiting clamp function may be a generalizable antibacterial strategy.
Insights
This study reveals a novel bacterial toxin-antitoxin system where the toxin SocB targets replication forks by interacting with the sliding clamp. This interaction disrupts DNA replication, offering a potential new antibacterial strategy.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Toxin-antitoxin (TA) systems are widespread in bacteria, crucial for various cellular processes, but their regulatory mechanisms and toxin targets are not fully understood.
- Understanding TA systems provides insights into bacterial survival and potential antimicrobial targets.
Purpose of the Study:
- To identify and characterize a novel toxin-antitoxin system, SocAB, in Caulobacter crescentus.
- To elucidate the mechanism of action and molecular target of the toxin SocB.
Main Methods:
- Genetic analysis of the SocAB system in Caulobacter crescentus.
- Biochemical assays to determine toxin-antitoxin interactions and protease activity.
- Bacterial genetics and molecular biology techniques to analyze replication inhibition.
Main Results:
- Identified SocAB as an atypical TA system where antitoxin SocA acts as a proteolytic adaptor for toxin SocB degradation by ClpXP.
- Demonstrated that toxin SocB inhibits replication elongation by interacting with the sliding clamp, leading to replication fork collapse.
- Mapping of suppressor mutations indicated SocB competes with other proteins for binding to the sliding clamp's DNA polymerase III binding site.
Conclusions:
- The SocAB system represents a new class of TA systems with unique regulatory and functional mechanisms.
- SocB's inhibition of replication clamp function highlights a novel antibacterial strategy targeting essential replication processes.
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