Two mechanisms coordinate replication termination by the Escherichia coli Tus-Ter complex

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The Escherichia coli replication terminator protein (Tus) binds to specific Ter DNA sequences.
• Tus-Ter complexes act as directional blocks to DNA replication forks.
• Understanding the mechanism of Tus-Ter interaction is crucial for DNA replication regulation.

Purpose of the Study:

• To investigate the response of the heterologous phage T7 replisome to the Tus-Ter complex.
• To elucidate the molecular mechanisms underlying replication fork arrest by Tus-Ter.
• To determine the role of specific DNA bases and motor protein translocation polarity.

Main Methods:

• Single-molecule experiments.
• Transient state kinetics.
• Analysis of replisome components (helicase and polymerase) interactions with Tus-Ter.

Main Results:

• The T7 replisome is arrested at the non-permissive end of Tus-Ter via a composite mousetrap and dynamic clamp model.
• An unpaired cytosine (C6) is critical for arresting the replisome by forming a lock within the Tus protein.
• DNA polymerase and helicase exhibit differential blocking at permissive and non-permissive ends, indicating polarity sensitivity.

Conclusions:

• The Tus-Ter complex acts as a polar DNA motor translocation sensor.
• Helicase-mediated strand separation and polymerase interaction with C6 are key to lock formation.
• This mechanism ensures precise termination of DNA replication.