ParABS partition systems, comprising the centromere-like DNA sequence , the -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 and move by generating and following a local concentration gradient of nucleoid-bound ParA. However, the process through which ParB activates ParA-ATPase has not been defined. We studied CTP- and -modulated ParA-ParB complex assembly, in which DNA-bound ParA-ATP dimers are activated for ATP hydrolysis by interacting with two ParB N-terminal domains. CTP or enhances the ATPase rate without significantly accelerating ParA-ParB complex assembly. Togeth... More
ParABS partition systems, comprising the centromere-like DNA sequence , the -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 and move by generating and following a local concentration gradient of nucleoid-bound ParA. However, the process through which ParB activates ParA-ATPase has not been defined. We studied CTP- and -modulated ParA-ParB complex assembly, in which DNA-bound ParA-ATP dimers are activated for ATP hydrolysis by interacting with two ParB N-terminal domains. CTP or enhances the ATPase rate without significantly accelerating ParA-ParB complex assembly. Together, and CTP accelerate ParA-ParB assembly without further significant increase in ATPase rate. Magnetic-tweezers experiments showed that CTP promotes multiple ParB loading onto -containing DNA, generating condensed partition complex-like assemblies. We propose that ParB in the partition complex adopts a conformation that enhances ParB-ParB and ParA-ParB interactions promoting efficient partitioning.
