The mechanisms of DNA replication in E. coli ensure that each daughter cell gets one copy of its genome.

When the bacterium E. coli divides, it needs to ensure that its circular chromosome is copied and one copy of each sister chromosome ends up in each daughter cell. Professor David Sherratt and colleagues at the University of Oxford have discovered how it manages to achieve this feat.

DNA replication in E. coli starts at a single point, the so-called origin of replication, and progresses in opposite directions around the circular chromosome, thereby creating two replicating 'arms'.

Using fluorescent dyes to visualise specific positions on the chromosome, the Oxford group could track the position of multiple genetic loci in cells and follow their fate after replication.

In resting cells, the positions of genetic loci tie in with the genetic map, with loci on the left arm positioned in one half of the cell and loci on the other arm found on the opposite side of the cell; the replication origin is close to the middle of the cell.

As the DNA is replicated on each arm, newly replicated sister loci segregate to distant regions of the cell, so that the emerging new daughter chromosomes are shunted to opposite halves of the dividing cell. When the parent cell finally divides, therefore, one chromosome is neatly parcelled into each new daughter cell.

External links

• Wang X et al. The two Escherichia coli chromosome arms locate to separate cell halves. Genes Dev 2006;20(13):1727–31.