| Whereas ample evidence has demonstrated that eukaryotic chromosomes can exhibit higher order organization, little evidence has been presented as to whether prokaryotic chromosomes are organized globally. This thesis investigates the chromosome organization and dynamics of two bacteria, Streptomyces coelicolor and Bacillus subtilis. Both studies employed fluorescence in situ hybridization. The ends of the Streptomyces chromosome were shown to associate in situ. Association of the chromosomal termini provides an explanation of how a linear bacterial chromosome is able to exhibit circular genetic behavior. Cytological evidence presented previously strongly suggests that in B. subtilis chromosome segregation occurs by an active mechanism. I investigated B. subtilis chromosome dynamics in detail. The locations and the dynamics of the DNA replication origin and terminus were described, and locations of events during the replication and segregation cycle were analyzed. Three conclusions were reached: (1) initiation of replication was found to occur at an off-center position in cells growing with a long doubling time, (2) separation of the duplicated chromosomes was found to start from the origin region, and (3) the distance between the duplicated sister origins was found to increase as cell length increased. |
