| Cellular division is a requirement for all life and cannot be achieved without proper partitioning of the genetic material to the daughter cells. Chromosome segregation must therefore be a robust process. Eukaryotes utilize a series of checkpoints and active segregation mechanisms to achieve the required accuracy, and these mechanisms are generally well understood. Prokaryotic chromosome segregation is also accurate and robust. However, how bacteria accurately segregate their chromosomes remains mysterious. Previous work has implicated many mechanisms, but none of these mechanisms can alone explain chromosome segregation in its entirety. Furthermore, the assumption that a single mechanism mediates segregation has caused proposed models to appear in conflict. In this dissertation we first show that both MreB and the par system function in chromosome segregation in Caulobacter crescentus. Simultaneous perturbation of both systems resulted in a synthetic defect in ori translocation. Thus, in Caulobacter, chromosome segregation is a multi-mechanistic process. Next, we characterized the dynamics of the chromosomal origin region ( ori) during segregation, and found that it is a complex motion with four individual steps: polar release, polar retraction, and early and late translocation. Perturbation of the par system indicated that it is specifically required for only late translocation. We hypothesize that the steps may be mediated by different mechanisms with the overall function to ensure the fidelity of chromosome segregation. |
