Delineation of the Ancestral Tus-Dependent Replication Fork Trap

Area of Science:

• Molecular Biology
• Genomics
• Microbiology

Background:

• DNA replication termination in Escherichia coli relies on Ter sites and Tus proteins to form a replication fork trap.
• The precise number and arrangement of functional Ter sites have been debated, with some sites showing no replication fork arrest.
• Understanding the minimal functional Tus-Ter system is crucial for comprehending genome stability.

Purpose of the Study:

• To investigate the genome-wide distribution and binding of Tus proteins to Ter sites in Escherichia coli.
• To determine the essential components of the ancestral DNA replication fork trap.
• To explore the diversity of replication fork trap architectures in Enterobacterales.

Main Methods:

• Genome-wide analysis of Tus protein distribution.
• Experimental testing of ectopic Ter site insertion.
• Comparative genomic analysis of Ter site arrangements across Enterobacterales.

Main Results:

• Only the six innermost Ter sites (TerA-E and G) are significantly bound by Tus.
• Ectopic insertion of a single TerB site in a non-permissive orientation was unsuccessful, indicating no requirement for backup sites.
• A novel replication fork trap architecture was identified in Enterobacterales outside the Enterobacteriaceae family.

Conclusions:

• The ancestral Tus-dependent DNA replication fork trap is minimal, consisting of only two Ter sites.
• The functional significance of additional Ter sites is limited, and backup sites are not necessary.
• Replication fork trap architectures exhibit significant diversity across bacterial species.