What is it about?
We investigated how Escherichia coli copies its chromosome after UV light damages the DNA. By following the chromosome origin and terminus, measuring DNA synthesis, and tracking newly made DNA across the chromosome, we found that existing replication forks stop or slow dramatically for at least 15–20 minutes before replication resumes. During this delay, undamaged origins of replication continue to fire through the normal DnaA-dependent pathway, and UV also triggers additional DnaA-independent DNA synthesis. All DNA synthesis after UV required DnaC, suggesting that recovery of blocked forks depends on loading the DnaB replicative helicase and possibly assembling new replication machinery. When nucleotide excision repair was absent, replication and cell division were delayed much longer, although some replication could still eventually resume.
Featured Image
Why is it important?
This study helps clarify what happens when bacterial replication forks meet UV-induced DNA lesions. It suggests that total DNA synthesis measurements can hide a real delay at pre-existing forks, because new origin firing and UV-induced synthesis add to the signal. The work supports a model in which E. coli delays restart while lesions are removed, which may reduce the need for excessive recombination during chromosome duplication.
Perspectives
What stands out to us is that the answer became clear only when we separated different sources of DNA synthesis. Fluorescent origin–terminus tracking, BrdU labelling, DnaA and DnaC mutants, and excision-repair-defective cells all pointed to the same conclusion: UV damage stalls ongoing replication more substantially than simple bulk DNA synthesis assays suggest. We find this useful because it gives a more balanced view of bacterial DNA damage recovery, where origin firing continues but stalled forks still need time and processing before chromosome replication can be completed.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Replication fork stalling and cell cycle arrest in UV-irradiated Escherichia coli, Genes & Development, March 2007, Cold Spring Harbor Laboratory Press,
DOI: 10.1101/gad.417607.
You can read the full text:
Contributors
The following have contributed to this page
