What is it about?
In this review, we examine how bacterial cells bring chromosome replication to a safe finish when the two DNA-copying machines meet. We focus mainly on circular bacterial chromosomes, especially Escherichia coli and Bacillus subtilis, where replication usually starts from one origin and ends when two replication forks fuse. We discuss evidence that fork fusion can create DNA intermediates, including short exposed DNA ends called 3′ flaps, that may trigger over-replication, recombination and problems with chromosome segregation if they are not contained. We highlight how fork trap systems such as Tus-ter in E. coli and RTP-ter in B. subtilis may help confine these events to a defined terminus region, where proteins such as RecG and nucleases can help process them. We also compare this bacterial organisation with archaeal and eukaryotic replication, where multiple origins and different helicase systems may change the nature of termination.
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Why is it important?
Replication termination is less well understood than replication initiation, yet this final step may itself create risks for genome stability. The review suggests that bacterial chromosome architecture, including one main origin, defined replichores and, in some species, a fork trap, could help limit where potentially harmful fork-fusion intermediates arise. This may explain why fork trap systems are not universal across bacteria, but appear to be strongly maintained in lineages that have acquired them.
Perspectives
What stands out to us is that the end of DNA replication is not simply a passive meeting of two forks. By bringing together evidence from fork trap architecture, RecG and exonuclease studies, over-replication patterns, chromosome dimer resolution and comparisons across organisms, we could frame termination as an active and potentially vulnerable stage of genome duplication. We also found it interesting that fork traps can create problems when replication becomes asynchronous, yet may still provide a cleaner way to contain and process fork-fusion intermediates. This review helped us place bacterial replication termination in a broader context without assuming that bacteria, archaea and eukaryotes all solve the problem in the same way.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Interplay between chromosomal architecture and termination of DNA replication in bacteria, Frontiers in Microbiology, June 2023, Frontiers,
DOI: 10.3389/fmicb.2023.1180848.
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