Distinct architectural requirements for the centromeric sequence of the pSM19035 plasmid partition machinery.

Three-component ParABS partition systems ensure stable inheritance of many bacterial chromosomes and low-copy-number plasmids. ParA localizes to the nucleoid through its ATP-dependent nonspecific DNA-binding activity, whereas centromere-like -DNA and ParB form partition complexes that activate ParA-ATPase to drive the system dynamics. The essential sequence arrangements vary among ParABS systems, reflecting the architectural diversity of their partition complexes. Here, we focus on the pSM19035 plasmid partition system that uses a ParB of the ribbon-helix-helix (RHH) family. We show that with four or more contiguous ParB-binding sequence repeats is required to assemble a stable ParA-ParB complex and efficiently activate the ParA-ATPase, stimulating complex disassembly. Disruption of the contiguity of the sequence array destabilizes the ParA-ParB complex and prevents efficient ATPase activation. Our findings reveal the unique architecture of the pSM19035 partition complex and how it interacts with nucleoid-bound ParA-ATP.