The organization of newly replicated E. coli chromosomes is described in a recent EMBO Journal paper by Solveig Fossum (first author), Elliot Crooke and Kirsten Skarstad. The current impact factor of EMBO Journal is 10.086.
A combined flow cytometry and fluorescence microscopy study showed that newly replicated sister origins were organized in a pairwise fashion. After a period of colocalization, sister origins were segregated in opposite directions.
Summary of the findings, from the authors:
In rapidly growing E. coli cells, the DNA replication period is longer than the generation time. In such cells, initiation of replication occurs at two or four origins in the “mother”- or “grandmother” generation respectively.
We have found that sister origins were colocalized within the cell for an entire generation or more whereas sister origins in slowly growing cells were colocalized only for 0.1-0.2 generations. Studies of replication fork organization also indicates colocalization of sister replication forks during rapid growth. Both findings indicate a higher order organization of DNA replication components in cells that grow with overlapping replication cycles.
The role of origin sequestration and the SeqA protein in this organization was also studied. The results indicate that correct organization of sister origins and sister replication forks is dependent on the binding of SeqA to newly formed DNA at the replication fork, but independent of origin sequestration.
Fossum S, Crooke E, Skarstad K.
Organization of sister origins and replisomes during multifork DNA replication inEscherichia coli.
EMBO J. 2007 Oct 4; [Epub ahead of print]
Home page of Kirsten Skarstad's group - Bacterial Cell Biology (radium.no/skarstad)
Institute for Cancer Research
Figure from the article (click to enlarge):