Conjugative plasmid-encoded toxin-antitoxin system PrpT/PrpA directly controls plasmid copy number

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Toxin-antitoxin (TA) systems are typically found on plasmids and contribute to plasmid stability through post-segregational killing.
• The known functions of plasmid-encoded TA systems primarily involve plasmid stabilization and competition, not direct control of replication.

Purpose of the Study:

• To investigate the function of the type II TA system, PrpT/PrpA, from Pseudoalteromonas rubra plasmid.
• To elucidate the mechanism by which this TA system influences plasmid maintenance and copy number.

Main Methods:

• Genetic deletion of the prpA-prpT operon.
• Analysis of plasmid copy number and replication control.
• Investigation of antitoxin PrpA binding to plasmid origin iterons.

Main Results:

• Deletion of the prpA-prpT operon increased plasmid copy number, contrary to typical TA system functions.
• Antitoxin PrpA acts as a negative regulator of plasmid replication by inhibiting replication initiator binding.
• PrpA is produced in excess to prevent overreplication, and its degradation derepresses replication.

Conclusions:

• The PrpT/PrpA TA system directly regulates plasmid replication, a novel function for plasmid-encoded TA systems.
• This system provides new insights into the physiological roles and mechanisms of TA systems in plasmid biology.
• The conserved nature of the PrpT/PrpA system suggests widespread importance in conjugative plasmid maintenance.