Abstract
In Escherichia coli, DNA replication termination is orchestrated by two clusters of Ter sites forming a DNA replication fork trap when bound by Tus proteins. The formation of a ‘locked’ Tus–Ter complex is essential for halting incoming DNA replication forks. However, the absence of replication fork arrest at some Ter sites raised questions about their significance. In this study, we examined the genome-wide distribution of Tus and found that only the six innermost Ter sites (TerA–E and G) were significantly bound by Tus. We also found that a single ectopic insertion of TerB in its non-permissive orientation could not be achieved, advocating against a need for ‘back-up’ Ter sites. Finally, examination of the genomes of a variety of Enterobacterales revealed a new replication fork trap architecture mostly found outside the Enterobacteriaceae family. Taken together, our data enabled the delineation of a narrow ancestral Tus-dependent DNA replication fork trap consisting of only two Ter sites.
Highlights
Bacteria such as Escherichia coli and Bacillus subtilis utilise distinct DNA replication fork trap systems within their chromosomal terminus region [1]
We hypothesised that Ter insertions resulting in weak to moderate replication fork pausing would yield a measurable effect on bacterial growth rate, while Ter insertions yielding efficient ectopic fork arrest should be unviable
In our efforts to investigate the evolutionary divergence of the type I/II fork traps, we identified a unique group of Cedecea species within the Enterobacteriaceae family that uses a type I replication fork trap system with only two oppositely oriented Ter sites for
Summary
Bacteria such as Escherichia coli and Bacillus subtilis utilise distinct DNA replication fork trap systems within their chromosomal terminus region [1]. This is exemplified in E. coli by the presence of a cluster of five similar but distinct 23-bp Ter DNA sequences on each chromosomal arm, which have anti-helicase activity when they are bound by the replication termination protein Tus [1,2,3]. The second cluster, which is oppositely oriented, consists of TerA, D, E, I, H and arrests the anticlockwise moving replication fork (Figure 1A). Binding of Tus to the pseudo-Ter sites is likely to be insignificant based on their sequences [5] and fork arrest efficiency [6]
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