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  • Book
    Sun-Hae Hong.
    Digital2011
    Replication and segregation of the chromosome in the bacterium Caulobacter crescentus takes place simultaneously. Although it is known that each arm of the circular chromosome is on average linearly positioned along the cell length, the detailed configuration of the DNA in the cell is not well understood. Furthermore, in replicating bacterial cells, the centromere is segregated by a ParA-dependent mechanism and anchored at the pole, but the segregation mechanism for the rest of the chromosome is not known. To address these questions, I tracked the position and motion of multiple chromosomal loci both in non-replicating and replicating cells. By characterizing compaction of the DNA in non-replicating cells, I show that the DNA in the Caulobacter cells has the mean end-to-end distance that scale as (contour length)0.22, which suggests that compaction of the bacterial DNA is primarily driven by supercoiling. Analysis of the replication/segregation dynamics revealed that Caulobacter chromosome segregation is bimodal: Centromere-proximal DNA is segregated with the centromere at a slow pace whereas the rest of the DNA is segregated much faster. The dynamics of the centromere-distal DNA are consistent with a model where continuous compaction pulls the DNA toward the pole. The results provide a new perspective on the physical configuration of the non-replicating DNA and on the movement and compaction of newly replicated DNA immediately after replication and during its transport from the replisome to the cell poles.