Chromosome Arrangement and Segregation
Peter L. Graumann
from: Bacillus: Cellular and Molecular Biology (Third edition) (Edited by: Peter L. Graumann). Caister Academic Press, U.K. (2017) Pages: 67-88.
After a bit more than a decade of the use of GFP - or immuno-fluorescence microscopy to study bacterial chromosome segregation, it has become clear that this process is highly organized, temporally as well as spatially, and that a machinery exists that mediates an overall gradual separation of sister chromosomes. Several key factors in this process have been identified, and at least a rough overall picture can be drawn on how chromosomes are separated so highly rapidly and efficiently. Bacillus subtilis has a circular chromosome. Replication initiates at the origin of replication that is defined as 0°, and two replication forks proceed bidirectionally to converge at the terminus region, which is defined as 180°. All other regions on the chromosome are defined as the corresponding site on a circle. DNA replication occurs in the cell centre, and duplicated regions are moved away from the cell centre towards opposite cell poles. How this process is energetically driven is still unknown, but entropic forces could play a major role. A dedicated protein complex called SMC forms two subcellular centres that organize newly duplicated chromosome regions within each cell half, setting up the spatial organization that characterizes bacterial chromosome segregation. Several proteins, including topoisomerases, DNA translocases and recombinases, ensure that entangled sister chromosomes or chromosome dimers can be completely separated into the future daughter cells shortly before cell division occurs at the middle of the cells read more ...