Abstract
Proper chromosome segregation during cell division is essential in all domains of life. In the majority of bacterial species, faithful chromosome segregation is mediated by the tripartite ParABS system, consisting of an ATPase protein ParA, a CTPase and DNA-binding protein ParB, and a centromere-like parS site. The parS site is most often located near the origin of replication and is segregated first after chromosome replication. ParB nucleates on parS before binding to adjacent non-specific DNA to form a multimeric nucleoprotein complex. ParA interacts with ParB to drive the higher-order ParB–DNA complex, and hence the replicating chromosomes, to each daughter cell. Here, we review the various models for the formation of the ParABS complex and describe its role in segregating the origin-proximal region of the chromosome. Additionally, we discuss outstanding questions and challenges in understanding bacterial chromosome segregation.
Highlights
Faithful chromosome segregation is essential to ensure each daughter cell inherits a full copy of the genetic information of the parent
We focus on progress towards understanding the molecular basis for segregating the origin-proximal region, by the tripartite ParA–ParB–parS system
In Caulobacter crescentus, Hyphomonas neptunium and Myxococcus xanthus, genes encoded in the par locus (ParABS) were found to be essential for cell viability [8,9,10,11], whereas in other bacterial species engineered strains lacking ParABS were viable but had an elevated number of anucleate cells owing to defects in chromosome segregation [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]
Summary
Faithful chromosome segregation is essential to ensure each daughter cell inherits a full copy of the genetic information of the parent. ParB binding to parS nucleates the recruitment of additional ParB molecules which associate with neighbouring DNA, a process known as spreading, to form a higher-order ParBDNA nucleoprotein complex [30]. The purpose of this higher-order complex, whether to strengthen the physical link between DNA and ParA or to provide a specific DNA topology to facilitate DNA segregation, is still under debate. Since bacterial strains harbouring nucleation competent but spreading-defective mutants of parB are either unviable or have elevated number of anucleate cells, it is clear that a higher-order nucleoprotein complex is a prerequisite for faithful chromosome segregation [7,47,48,49,50]. We describe and discuss the current and emerging models for the assembly of this essential nucleoprotein complex
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