Defining the prototypical DNA replication fork trap in bacteria
In Escherichia coli, DNA replication termination is orchestrated by two opposite 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. 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 ectopic insertion of a TerB sequence in its non-permissive orientation could not be achieved, advocating against the necessity for 'back-up' Ter sites due to the inefficient formation of a 'locked' Tus-Ter complex. Finally, examination of the genomes of a variety of Enterobacterales revealed two major types of replication fork traps including a prototypical architecture consisting of two unique Ter sequences in opposite orientation.