Replication Termination inEscherichia coli: Structure and Antihelicase Activity of the Tus-TerComplex

Abstract

The arrest of DNA replication in Escherichia coli is triggered by the encounter of a replisome with a Tus protein-Ter DNA complex. A replication fork can pass through a Tus-Ter complex when traveling in one direction but not the other, and the chromosomal Ter sites are oriented so replication forks can enter, but not exit, the terminus region. The Tus-Ter complex acts by blocking the action of the replicative DnaB helicase, but details of the mechanism are uncertain. One proposed mechanism involves a specific interaction between Tus-Ter and the helicase that prevents further DNA unwinding, while another is that the Tus-Ter complex itself is sufficient to block the helicase in a polar manner, without the need for specific protein-protein interactions. This review integrates three decades of experimental information on the action of the Tus-Ter complex with information available from the Tus-TerA crystal structure. We conclude that while it is possible to explain polar fork arrest by a mechanism involving only the Tus-Ter interaction, there are also strong indications of a role for specific Tus-DnaB interactions. The evidence suggests, therefore, that the termination system is more subtle and complex than may have been assumed. We describe some further experiments and insights that may assist in unraveling the details of this fascinating process

Essential Biological Processes of an Emerging Pathogen: DNA Replication, Transcription, and Cell Division in Acinetobacter spp

“…The DnaB helicase translocates on the lagging strand at each fork. DNA replication continues bidirectionally around the circular chromosome until the two replication forks meet in the terminus region, located approximately opposite the origin (182,189). This eventually yields two copies of the bacterial chromosome, each containing one strand from the parental chromosome and one nascent strand.…”

Regulation of Recombination and Genomic Maintenance

“…A particular problem specific to eukaryotes and organisms with linear genomes is replication termination. Although circular genomes have defined termination sites and dedicated mechanisms (Neylon et al 2005), equivalent systems are lacking in eukaryotes. On one hand, this provides greater flexibility in eukaryotes, as replication forks will eventually converge.…”

Mechanisms and Controls of DNA Replication in Bacteria

“…These sites are physically arranged in positions opposite to the oriC ( Figure 5). In the collision of Tus with the helicase a trap is formed that prevents the further advancement of the replicative machinery in the leading strand and remains arrested until the replicative machinery on the lagging strand reaches this position (Neylon et al, 2005). The elongation of DNA in the E. coli chromosome is carried out in both directions of the fork by a multisubunit machinery called the replisome.…”