Abstract
Chromosome segregation is an essential cellular function in eukaryotic and prokaryotic cells. The ParABS system is a fundamental player for a mitosis-like process in chromosome partitioning in many bacterial species. This work shows that the social bacterium Myxococcus xanthus also uses the ParABS system for chromosome segregation. Its large prokaryotic genome of 9.1 Mb contains 22 parS sequences near the origin of replication, and it is shown here that M. xanthus ParB binds preferentially to a consensus parS sequence in vitro. ParB and ParA are essential for cell viability in M. xanthus as in Caulobacter crescentus, but unlike in many other bacteria. Absence of ParB results in anucleate cells, chromosome segregation defects and loss of viability. Analysis of ParA subcellular localization shows that it clusters at the poles in all cells, and in some, in the DNA-free cell division plane between two chromosomal DNA masses. This ParA localization pattern depends on ParB but not on FtsZ. ParB inhibits the nonspecific interaction of ParA with DNA, and ParA colocalizes with chromosomal DNA only when ParB is depleted. The subcellular localization of ParB suggests a single ParB-parS complex localized at the edge of the nucleoid, next to a polar ParA cluster, with a second ParB-parS complex migrating after the replication of parS takes place to the opposite nucleoid edge, next to the other polar ParA cluster.
Highlights
Genetic information is written in long DNA molecules
In Escherichia coli, a higherorder structure of chromosomal DNA has been described, with a length between 0.8 to 1 Mb, which is organized by MatP protein and multiple matS DNA sequences [4]
The main objective of this work was to ascertain if the DNA sequences that encode the predicted ParABS elements, taken from the M. xanthus genome annotation, have a role in chromosome segregation in M. xanthus
Summary
Genetic information is written in long DNA molecules. A typical bacterial chromosome extends to a length over a thousand times greater than the cell in which it resides. It is assumed that a chromosomal ParABS system, originally described in plasmids, acts as a mitotic-like apparatus to segregate replicated chromosomes [1,2,14]. The second component of ParABS systems, protein ParB, binds to the parS sites to form a large nucleoprotein complex near oriC as well as to the third component of the system, ParA. The latter is an ATPase proposed as the element that provides the force for the segregation of the ‘‘centromeric’’ parS sites via dynamic polymerization-depolymerization events [2,14,16,17,18]. Genes encoding parA and parB are usually found in the oriC-proximal regions of the chromosome, and they have been shown to participate in proper chromosome partitioning in numerous bacteria [15,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
