Caulobacter requires a dedicated mechanism to initiate chromosome segregation

Abstract

Chromosome segregation in bacteria is rapid and directed, but the mechanisms responsible for this movement are still unclear. We show that Caulobacter crescentus makes use of and requires a dedicated mechanism to initiate chromosome segregation. Caulobacter has a single circular chromosome whose origin of replication is positioned at one cell pole. Upon initiation of replication, an 8-kb region of the chromosome containing both the origin and parS moves rapidly to the opposite pole. This movement requires the highly conserved ParABS locus that is essential in Caulobacter. We use chromosomal inversions and in vivo time-lapse imaging to show that parS is the Caulobacter site of force exertion, independent of its position in the chromosome. When parS is moved farther from the origin, the cell waits for parS to be replicated before segregation can begin. Also, a mutation in the ATPase domain of ParA halts segregation without affecting replication initiation. Chromosome segregation in Caulobacter cannot occur unless a dedicated parS guiding mechanism initiates movement.centromere ͉ parS ͉ ParA

Rapid pairing and resegregation of distant homologous loci enables double-strand break repair in bacteria

“…In contrast, in undamaged, wildtype cells, ParA(K20R) prevents the full segregation of newly replicated origins to opposite cell poles, but the origin regions still separate and two distinct foci can be resolved (Toro et al, 2008;Shebelut et al, 2010). Thus, we suggest that the initial separation of newly replicated origins may depend on DNA replication, with the physical act of replication and bulk chromosome accumulation potentially providing the force, and ParA then driving complete segregation.…”

Cell pole–specific activation of a critical bacterial cell cycle kinase

“…LacZ synthesis was measured by performing [ 35 S]-methionine pulse experiments as described previously (26). Before G1-phase cell synchrony [performed as described previously (27)], the culture was incubated with 0.3% xylose overnight, and xylose was present during the [ 35 S]-methionine pulse experiment.…”

Independent Segregation of the Two Arms of theEscherichia coli oriRegion Requires neither RNA Synthesis nor MreB Dynamics

“…ParA is an ATPase that binds ParB and is proposed to direct the ParB/parS complex to the poles (18). These partitioning systems serve to facilitate chromosome segregation but are often not essential, for example, in B. subtilis, Streptomyces coelicolor, and Pseudomonas putida and for V. cholerae chromosome I (18,23,30,35).In contrast, these systems are essential for viability in C. crescentus (41,54) and for segregation of chromosome II in V. cholerae (63). The latter requirement may be due to the fact that chromosome II has many properties of a large plasmid and its Par proteins are more closely related to plasmid-encoded ones than to those encoded on chromosomes (22).…”

“…In contrast, these systems are essential for viability in C. crescentus (41,54) and for segregation of chromosome II in V. cholerae (63). The latter requirement may be due to the fact that chromosome II has many properties of a large plasmid and its Par proteins are more closely related to plasmid-encoded ones than to those encoded on chromosomes (22).…”