Principal Investigator Alan Grossman
Cells invest significant resources in the faithful replication and partitioning of chromosomes. Chromosome duplication involves assembly of a large complex of proteins at an origin (at 0° on the B. subtilis circular chromosome) and processive replication in both directions away from the origin. Our work studying replication in vivo indicated that during replication, the DNA moves to the DNA replication machinery (the replisome), gets duplicated, and then moves away. This is in contrast to models in which the replication machinery moves along the DNA.
To gain insight into the spatial and temporal organization of the replication cycle, we visualized replication origins and the replication machinery (replisomes) inside live cells. Our analysis indicates that the location of the origin at the time of replication initiation establishes the position of the replisome. Also, it appears that sister replication forks are not intimately associated with each other throughout the replication cycle. We also found that the subcelluar location of the 0° region of the chromosome does not require the presence of an active origin of replication, nor does it require sequences within the origin itself. We also found that this positioning is independent of the replication initiation protein DnaA. This work indicates that there as yet uncharacterized factors involved in chromosome positioning and orientation.