What is it about?
We investigated what happens to Escherichia coli cells lacking RecG, a DNA translocase involved in replication, repair and recombination, after they are exposed to UV damage. Although these cells remove UV-induced DNA lesions at about the normal rate, they show a long delay in cell division and persistent problems separating their chromosomes. We found that this is linked to high levels of DnaA-independent stable DNA replication, meaning DNA synthesis that starts away from the normal chromosome origin. This abnormal replication depends strongly on PriA helicase activity and is reduced when PriA helicase is inactivated or when RecG is reintroduced. Our results support a model in which extra replication forks collide outside the normal terminus region, creating DNA structures that can seed further inappropriate replication and chromosome amplification.
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Why is it important?
This study suggests that finishing bacterial chromosome replication is not simply a passive meeting of two replication forks. It helps explain why E. coli normally starts replication from a single origin and restricts fork encounters to a defined terminus region. The work also shows that apparent survival after UV damage can mask serious defects in DNA replication, chromosome segregation and cell-cycle recovery.
Perspectives
What stands out to us is that the recG cells were not failing because UV lesions remained unrepaired; rather, they were making too much DNA in the wrong way. Combining time-lapse microscopy, origin–terminus tracking, DNA synthesis assays and PriA helicase mutants allowed us to connect the cell-shape defects with pathological stable DNA replication. This paper helped us view RecG not only as a protein involved in recombination, but also as a factor that helps keep chromosome replication orderly when replication forks are restarted or redirected.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Pathological replication in cells lacking RecG DNA translocase, Molecular Microbiology, August 2009, Wiley,
DOI: 10.1111/j.1365-2958.2009.06773.x.
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