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Genes 2018, 9(8), 376; https://doi.org/10.3390/genes9080376

Origins Left, Right, and Centre: Increasing the Number of Initiation Sites in the Escherichia coli Chromosome

1
Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
2
School of Life Sciences, University of Warwick, Gibbet Hill Campus, Coventry CV4 7AL, UK
3
Department of Science and Environment, Roskilde University, DK-4000 Roskilde, Denmark
*
Author to whom correspondence should be addressed.
Received: 27 June 2018 / Revised: 20 July 2018 / Accepted: 23 July 2018 / Published: 27 July 2018
(This article belongs to the Special Issue Chromosome Replication and Genome Integrity)
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Abstract

The bacterium Escherichia coli contains a single circular chromosome with a defined architecture. DNA replication initiates at a single origin called oriC. Two replication forks are assembled and proceed in opposite directions until they fuse in a specialised zone opposite the origin. This termination area is flanked by polar replication fork pause sites that allow forks to enter, but not to leave. Thus, the chromosome is divided into two replichores, each replicated by a single replication fork. Recently, we analysed the replication parameters in E. coli cells, in which an ectopic origin termed oriZ was integrated in the right-hand replichore. Two major obstacles to replication were identified: (1) head-on replication–transcription conflicts at highly transcribed rrn operons, and (2) the replication fork trap. Here, we describe replication parameters in cells with ectopic origins, termed oriX and oriY, integrated into the left-hand replichore, and a triple origin construct with oriX integrated in the left-hand and oriZ in the right-hand replichore. Our data again highlight both replication–transcription conflicts and the replication fork trap as important obstacles to DNA replication, and we describe a number of spontaneous large genomic rearrangements which successfully alleviate some of the problems arising from having an additional origin in an ectopic location. However, our data reveal additional factors that impact efficient chromosome duplication, highlighting the complexity of chromosomal architecture. View Full-Text
Keywords: DNA replication; replication termination; ter/Tus complex; replication-transcription conflicts; chromosome dynamics; bacterial chromosome structure DNA replication; replication termination; ter/Tus complex; replication-transcription conflicts; chromosome dynamics; bacterial chromosome structure
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Dimude, J.U.; Stein, M.; Andrzejewska, E.E.; Khalifa, M.S.; Gajdosova, A.; Retkute, R.; Skovgaard, O.; Rudolph, C.J. Origins Left, Right, and Centre: Increasing the Number of Initiation Sites in the Escherichia coli Chromosome. Genes 2018, 9, 376.

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