Segrosome assembly at the pliable parH centromere

Area of Science:

• Bacterial plasmid biology
• Molecular mechanisms of DNA segregation
• Protein-DNA interactions

Background:

• Multiresistance plasmids utilize complex protein machinery for stable inheritance.
• The TP228 plasmid's segrosome, composed of ParF and ParG, is crucial for its segregation.
• Understanding the parH centromere's structure and function is key to plasmid stability.

Purpose of the Study:

• To elucidate the structural organization and functional dynamics of the parH centromere site.
• To investigate the roles of ParG and ParF in binding and organizing the centromere.
• To determine how these interactions influence plasmid segregation.

Main Methods:

• Site-directed mutagenesis and deletion analysis of the parH site.
• In vivo characterization of centromere function with modified parH sequences.
• Biochemical analysis of ParG and ParF binding to parH DNA.

Main Results:

• The parH centromere comprises degenerate tetramer boxes and AT-rich spacers, lacking intrinsic curvature.
• ParG binds cooperatively to parH via its N-terminal tails and ribbon-helix-helix domain, with AT-rich spacers mediating indirect readout.
• ParF interacts with ParG, not directly with parH, and modulates centromere conformation for segrosome assembly.

Conclusions:

• The parH centromere exhibits significant in vivo elasticity, accommodating various geometries for effective centromere activity.
• ParG's N-terminal tails and ribbon-helix-helix domain are essential for specific and cooperative parH binding.
• ParF's assembly into the segrosome is dependent on ParG's flexible tails, highlighting a coordinated mechanism for plasmid segregation.