What is it about?
DNA replication is essential for all living cells, ensuring that genetic information is accurately copied before cell division. It is usually assumed that when replication finishes, the process is completed cleanly: replication forks meet, the DNA strands are joined, and the chromosome is fully intact. This study challenges that view. We investigated what happens when two DNA replication forks meet during the final stage of replication, known as termination. Using a controlled system in E. coli, we were able to trigger fork fusion at defined locations and measure its consequences. We found that these termination events lead to a measurable increase in genetic recombination, even in otherwise normal cells with fully functional DNA replication and repair systems. This shows that DNA replication termination is not simply a passive endpoint. Instead, the meeting of replication forks can itself destabilise the genome, creating opportunities for unwanted DNA rearrangements. While cells have mechanisms to limit these effects, our results demonstrate that the risk is inherent to the process of completing DNA replication. We also explored how different DNA processing pathways influence these events, showing that certain factors can amplify the instability. However, the key finding is that the underlying effect is already present in normal cells. Overall, this work revises our understanding of DNA replication by identifying termination as a built-in source of genomic instability, rather than a perfectly resolved final step.
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Why is it important?
DNA replication underpins all life, and maintaining genome stability is essential for preventing mutations, disease and cell dysfunction. Most models assume that replication is highly accurate from start to finish, with particular attention paid to problems that occur during elongation, such as stalled or collapsed replication forks. In contrast, the final step – when replication forks meet – has generally been viewed as a routine process. Our findings show that this assumption is wrong. We demonstrate that the completion of DNA replication is inherently risky, with fork fusion events capable of triggering genetic recombination even in normal cells. This means that genome instability is not only a consequence of replication errors or defective repair systems, but can arise from the normal process of finishing replication itself. This has important implications for how we understand the origins of mutations and genome rearrangements. If termination is intrinsically destabilising, then cells must constantly manage and limit these effects, rather than simply responding to rare failures. It highlights how genome maintenance is continuously involved in all stages of the duplication process, including termination. Although this study was carried out in bacteria, DNA replication is fundamentally conserved across all domains of life. The principles uncovered here may therefore extend to more complex organisms, where genome instability is linked to ageing, cancer, and other diseases. By identifying replication termination as a previously underappreciated source of instability, this work opens new directions for understanding how genomes are maintained and why they sometimes fail.
Perspectives
A key motivation behind this work was to challenge a long-standing assumption in the field: that DNA replication ends cleanly when replication forks meet. What surprised us was not just that instability can arise at these sites, but that it is detectable even in otherwise normal cells. This suggests that genome instability is not only the result of failures in replication or repair, but is inherent to the process of completing DNA replication itself. One reason this point may be overlooked is that more dramatic effects are seen when specific pathways are disrupted. However, these perturbations amplify an underlying phenomenon that is already present under normal conditions. In that sense, termination is not an occasional problem, but a fundamental vulnerability that cells must continuously manage. I have discussed the broader implications of this idea, and how it changes our view of genome stability, in more detail here: https://rudolphlab.com/blog/the-dangerous-art-of-completing-the-task
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Termination of DNA replication drives genomic instability via multiple mechanisms, Nucleic Acids Research, January 2026, Oxford University Press (OUP),
DOI: 10.1093/nar/gkaf1519.
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