Quantitative model of ColE1 plasmid copy number control

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Plasmid replication initiation in E. coli, specifically ColE1, is regulated by interactions between RNA I and RNA II.
• The plasmid-encoded Rom protein enhances the formation of a complex between RNA I and RNA II, inhibiting replication.
• Previous studies focused on in vitro kinetics, but in vivo dynamics required further investigation.

Purpose of the Study:

• To develop a dynamic model for the in vivo replication control mechanism of the E. coli plasmid ColE1.
• To account for measured in vivo concentrations and half-lives of regulatory RNAs and proteins.
• To deduce a formula for steady-state plasmid concentration and identify key regulatory parameters.

Main Methods:

• Development of a dynamic model incorporating measured in vivo concentrations of RNA I, RNA II, and Rom protein.
• Analysis of the model to derive a formula for steady-state plasmid concentration.
• Comparison of model predictions with previous theoretical analyses and experimental data.

Main Results:

• The model confirms that plasmid copy number strongly depends on the RNA I synthesis rate.
• New predictions indicate significant influence of the RNA I-RNA II complex formation rate constant on copy number.
• Plasmid copy number increases linearly with RNA II synthesis rate and host generation time; Rom protein modulates but does not qualitatively alter control.

Conclusions:

• The dynamic model provides quantitative predictions for plasmid copy number, including increases in rom- mutants.
• The rate of initial unstable complex formation is a critical determinant of plasmid copy number.
• Further experiments are proposed to validate the model's predictions regarding replication control mechanisms.