Prevention of RK2 plasmid replication initiation in starved Escherichia coli cells

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacterial adaptation to environmental stress involves regulating DNA replication.
• Mechanisms controlling chromosomal replication under stress are known, but plasmid replication control is not.

Purpose of the Study:

• Investigate how amino acid starvation impacts RK2 plasmid replication in E. coli.
• Identify the roles of plasmid initiator TrfA and host initiator DnaA in this process.

Main Methods:

• Studied RK2 plasmid replication in E. coli under amino acid starvation.
• Analyzed the binding of TrfA and DnaA to the RK2 origin of replication (oriV).
• Assessed plasmid DNA levels and TrfA protein concentrations.

Main Results:

• Amino acid starvation prevents TrfA and DnaA binding to oriV, inhibiting RK2 replication.
• No increase in plasmid DNA levels was detected, indicating replication initiation failure.
• A hyperactive TrfA variant also failed to initiate replication, suggesting mechanisms beyond handcuffing are involved.
• TrfA and DnaA levels significantly decreased during stress, with TrfA reduction attributed to proteolysis.

Conclusions:

• RK2 plasmid replication is inhibited during amino acid starvation in E. coli.
• This inhibition is primarily due to a significant decrease in the intracellular concentrations of initiator proteins TrfA and DnaA.
• Proteolysis of TrfA represents a key regulatory mechanism controlling plasmid replication under stress.