Escherichia coli low-copy-number plasmid R1 centromere parC forms a U-shaped complex with its binding protein ParR.

Area of Science:

• Bacterial genetics
• Molecular biology
• Plasmid segregation

Background:

• The low-copy-number plasmid R1 in Escherichia coli utilizes a segregation machinery involving parC, ParR, and ParM.
• The parC site, analogous to a centromere, features two distinct repeat sets.

Purpose of the Study:

• To elucidate the structural organization of the parC/ParR complex using atomic force microscopy (AFM).
• To understand the binding stoichiometry and DNA bending induced by ParR interaction with parC iterons.

Main Methods:

• Atomic Force Microscopy (AFM) was employed to visualize the interaction between ParR proteins and the parC DNA site.
• Analysis of DNA fragment lengths and structural conformation of the parC/ParR complex.

Main Results:

• ParR molecules bind individually to each 5-fold repeat within parC, with a stoichiometry of approximately one ParR dimer per iteron.
• The parC/ParR complex adopts a U-shaped structure, with the DNA folding back at roughly 150 degrees.
• No intramolecular or intermolecular dimerization of ParR complexes was observed on parC DNA.

Conclusions:

• The ParR-parC interaction results in a specific DNA bending, forming a U-shaped complex.
• This structural organization is crucial for the plasmid segregation machinery in Escherichia coli.
• The findings provide insights into bacterial segregation complexes and suggest potential commonalities in their structure and function.