How RecFOR helps E. coli restart DNA replication after UV damage

What is it about?

We investigated how Escherichia coli resumes chromosome replication after UV light stalls replication forks, the DNA-copying structures that move along the chromosome. Using fluorescence microscopy and DNA labelling, we followed replication of the chromosome origin and terminus, overall DNA synthesis, and degradation of newly made DNA. We found that the RecFOR pathway, which helps place the RecA repair protein on exposed single-stranded DNA, is needed for efficient recovery of stalled forks. Replication from the normal origin and damage-triggered stable DNA replication, a form of DNA synthesis that starts away from the usual origin, were also delayed without RecFOR, but eventually recovered. Blocking DnaC-dependent loading of the main replication helicase caused similar DNA degradation even when RecFOR was present, while cells lacking DNA polymerase II did not show a major restart defect.

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Why is it important?

Stalled replication forks can leave newly made DNA vulnerable, so understanding how bacteria recover from this stress helps explain how genome integrity is maintained after DNA damage. Our results suggest that RecFOR and RecA may protect newly made DNA mainly by helping replication restart efficiently, rather than by acting simply as a static shield against nucleases. The work also supports a more cautious view of DNA polymerase II in this setting, suggesting that it is not essential for fork recovery under the conditions we tested.

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