Replisome speed determines the efficiency of the Tus−Ter replication termination barrier

• Published in: Nature (London) Vol. 525; no. 7569; pp. 394 - 398
• Main Authors: Elshenawy, Mohamed M., Jergic, Slobodan, Xu, Zhi-Qiang, Sobhy, Mohamed A., Takahashi, Masateru, Oakley, Aaron J., Dixon, Nicholas E., Hamdan, Samir M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.09.2015; Nature Publishing Group
• Subjects: 147/3; 631/337/151; 631/337/151/2353; 631/45/173; 631/57/2265; 82/103; 82/16; 82/83; Analysis; Base Sequence; Binding, Competitive; Chromosome replication; Chromosomes; Chromosomes, Bacterial - genetics; Chromosomes, Bacterial - metabolism; Crystallography, X-Ray; Deoxyribonucleic acid; DNA; DNA Replication; DNA synthesis; DNA-Directed DNA Polymerase - chemistry; DNA-Directed DNA Polymerase - metabolism; E coli; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; Humanities and Social Sciences; Kinetics; letter; Models, Biological; Models, Molecular; Movement; multidisciplinary; Multienzyme Complexes - chemistry; Multienzyme Complexes - metabolism; Protein Conformation; Proteins; Regulatory Sequences, Nucleic Acid - genetics; Science; Surface Plasmon Resonance; Time Factors; United States
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature14866

The Tus– Ter termination site of Escherichia coli is not completely efficient in stopping DNA replication, with about half of replisomes bypassing this blockade; here the speed of the replication machinery is shown to determine the outcome of the encounter between the replisome and Tus– Ter . DNA replication termination in a bacterium The bacterium Escherichia coli has a single origin of DNA replication, from which two replication complexes, or replisomes, move in opposite directions. They meet about half way round the single circular chromosome, at a termination region, Ter . The Ter site is bound by Tus protein, but this is not completely efficient in stopping replication; about half of the replisomes will bypass this blockade. Samir Hamdan and colleagues now show that a combination of the rate of replisome movement, and the dynamics of Tus interaction with Ter and its displacement, dictate termination efficiency. Consequently, it is the speed of the replication machinery that determines the outcome of the encounter. In all domains of life, DNA synthesis occurs bidirectionally from replication origins. Despite variable rates of replication fork progression, fork convergence often occurs at specific sites 1 . Escherichia coli sets a ‘replication fork trap’ that allows the first arriving fork to enter but not to leave the terminus region 2 , 3 , 4 , 5 . The trap is set by oppositely oriented Tus-bound Ter sites that block forks on approach from only one direction 3 , 4 , 5 , 6 , 7 . However, the efficiency of fork blockage by Tus– Ter does not exceed 50% in vivo despite its apparent ability to almost permanently arrest replication forks in vitro 8 , 9 . Here we use data from single-molecule DNA replication assays and structural studies to show that both polarity and fork-arrest efficiency are determined by a competition between rates of Tus displacement and rearrangement of Tus– Ter interactions that leads to blockage of slower moving replisomes by two distinct mechanisms. To our knowledge this is the first example where intrinsic differences in rates of individual replisomes have different biological outcomes.