ParAdependent

ParA-dependent refers to a class of bacterial DNA partitioning systems that rely on the ATPase ParA to ensure faithful segregation of DNA elements, most notably low-copy-number plasmids, and sometimes chromosomal regions, during cell division. The core components are ParA, an ATPase; ParB, a DNA-binding adaptor protein; and parS, a centromere-like DNA site typically located on the plasmid or on a specific chromosomal locus. In a ParA-dependent system, ParA binds ATP and associates with the bacterial nucleoid, forming a dynamic pattern or gradient. ParB bound to parS on the DNA cargo interacts with ParA, stimulating its ATP hydrolysis and causing ParA to dissociate from DNA. This cycle generates a directional force or guided movement of the ParB-parS cargo toward regions of different ParA-occupancy, effectively moving the plasmid or chromosomal element toward the daughter cell during division. Several mechanistic models exist, including diffusion–capture and a gradient-driven search-and-capture mechanism; the exact details can vary among species.

ParA-dependent partitioning systems are widespread in bacteria and are distinguished from ParM-based systems, which use an actin-like ParM protein for plasmid segregation. The ParA pathway robustly maintains plasmid copy number and genetic stability in populations, enabling faithful inheritance under diverse growth conditions. Variants of ParA-dependent systems can differ in regulatory inputs, localization patterns, and interactions with host factors, reflecting adaptation to different genomic contexts.