What is it about?
In this review, we examine how DNA replication ends in prokaryotes, especially in the circular chromosomes of Escherichia coli and Bacillus subtilis. We explain how two DNA-copying machines, called replication forks, move away from the origin of replication and eventually meet in a terminus region. In these bacteria, a replication fork trap made of Ter DNA sites and terminator proteins helps keep fork fusion within this region, although E. coli and B. subtilis use different proteins, Tus and RTP. We also discuss what happens after fork fusion, including separation of daughter chromosomes and evidence that poorly controlled termination can lead to unwanted copying of DNA that has already been replicated. Some archaea appear to handle termination differently, with multiple origins and no clear fork-trap system.
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Why is it important?
Replication termination can seem like the endpoint of chromosome copying, but the evidence reviewed here suggests it is an actively managed part of genome maintenance. The fork trap, RecG, single-strand DNA exonucleases, topoisomerases, and chromosome dimer resolution systems may all help cells finish replication without leaving chromosomes tangled, joined, or over-replicated. This helps explain why the final meeting of replication forks can matter for genome stability, not just for completing DNA synthesis.
Perspectives
What stands out to us is that E. coli and B. subtilis use independently evolved fork-arrest systems to control a similar chromosome-level problem. We also highlight that the role of the terminus region may be broader than simply preventing replication-transcription conflicts; it may help contain potentially harmful events that arise when replication forks fuse. The review is useful because it connects detailed molecular mechanisms, such as Tus–Ter and RTP–Ter fork arrest, with larger questions about chromosome organization, replication completion, and daughter chromosome separation.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Termination of DNA Replication in Prokaryotes, January 2019, Wiley,
DOI: 10.1002/9780470015902.a0001056.pub3.
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