CTP and <i>parS</i> coordinate ParB partition complex dynamics and ParA-ATPase activation for ParABS-mediated DNA partitioning.

Abstract

ParABS partition systems, comprising the centromere-like DNA sequence <i>parS</i>, the <i>parS</i>-binding ParB-CTPase, and the nucleoid-binding ParA-ATPase, ensure faithful segregation of bacterial chromosomes and low-copy-number plasmids. F-plasmid partition complexes containing ParB_F and <i>parS_F</i> move by generating and following a local concentration gradient of nucleoid-bound ParA_F. However, the process through which ParB_F activates ParA_F-ATPase has not been defined. We studied CTP- and <i>parS_F</i>-modulated ParA_F-ParB_F complex assembly, in which DNA-bound ParA_F-ATP dimers are activated for ATP hydrolysis by interacting with two ParB_F N-terminal domains. CTP or <i>parS_F</i> enhances the ATPase rate without significantly accelerating ParA_F-ParB_F complex assembly. Together, <i>parS_F</i> and CTP accelerate ParA_F-ParB_F assembly without further significant increase in ATPase rate. Magnetic-tweezers experiments showed that CTP promotes multiple ParB_F loading onto <i>parS_F</i>-containing DNA, generating condensed partition complex-like assemblies. We propose that ParB_F in the partition complex adopts a conformation that enhances ParB_F-ParB_F and ParA_F-ParB_F interactions promoting efficient partitioning.