ParAB

ParAB is a bacterial plasmid partitioning system that consists of two key proteins, ParA and ParB, along with a cis-acting centromere-like site called parS on the plasmid. The system ensures faithful segregation of low-copy-number plasmids to daughter cells during cell division.

ParB binds specifically to parS on the plasmid to form a partition complex. ParA is an ATPase that forms dynamic gradients on the nucleoid. Through interactions with the ParB-parS complex, ParA undergoes ATP-dependent changes that promote movement of the plasmid, effectively pulling or repositioning it toward opposite cell poles so that each daughter cell inherits copies of the plasmid.

ParAB systems are widespread in many bacteria, including both Gram-negative and Gram-positive species, and can be located on plasmids or, in some cases, on the chromosome. Variations exist across different systems, and some components may be referred to by alternate names such as SopA/SopB in related partitioning modules. ParA and ParB homologs are typically encoded near parS loci and are coordinated with replication to maintain plasmid stability in populations.

The ParAB mechanism is a focus of study in bacterial cell biology and has applications in synthetic biology, where stable plasmid inheritance is desirable for engineered strains. Understanding ParAB contributes to broader insights into how cells organize genetic material and ensure reliable inheritance across generations.