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Replication of Plasmid R1 during Downshift in Copy number.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Cell and Molecular Biology.
Manuscript (Other academic)
URN: urn:nbn:se:uu:diva-90568OAI: oai:DiVA.org:uu-90568DiVA: diva2:162962
Available from: 2003-04-29 Created: 2003-04-29 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Control of Chromosome and Plasmid Replication in Escherichia coli
Open this publication in new window or tab >>Control of Chromosome and Plasmid Replication in Escherichia coli
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Life is cellular. Cells grow and divide to give two new cells; this process is called the cell cycle. The chromosome in a bacterium is replicated into two identical copies before the cell divides. DNA replication is a fundamental process common to all forms of life.

In my thesis, I have studied control of chromosome and plasmid replication in Escherichia coli, a rod-shaped bacterium. Plasmids are extrachromosomal autonomously replicating DNA molecules.

I have combined the classical Meselson-Stahl density-shift and DNA hybridisation with theoretical analysis of DNA replication. The minimal time between two successive replications of the same molecule, the eclipse, was determined for both plasmid and chromosome.

The aim was to investigate the processes ensuring the precise timing of chromosome replication in the cell cycle. In wild-type strains, the chromosomal eclipse was long. Mutations affecting the so-called sequestration process, the superhelicity of the DNA, and the initiation protein, DnaA, reduced the eclipse.

Fast-growing E. coli has overlapping replicative phases with synchronous initiation from multiple initiation sites, oriC. I have investigated the complex interplay between different control processes by measuring the length of the eclipse and the degree of asynchronous initiation in various mutants.

I have measured the eclipse period of plasmid R1 during up- and down-shifts in plasmid copy number. The length of the eclipse was found to be determined by structural events as well as by the properties of the copy-number-control system.

During downshift from very high copy numbers, the rate of plasmid replication started very slowly and gradually increased until the normal copy number was achieved, in accordance with the +n model.

The CopB system of plasmid R1 was shown to be a rescue system preventing cells with few plasmid copies from losing the plasmid in some of the daughter cells.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 65 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 838
Microbiology, Mikrobiologi
National Category
Research subject
urn:nbn:se:uu:diva-3471 (URN)91-554-5627-8 (ISBN)
Public defence
2003-05-22, B:10, Biomedicinskt Centrum BMC, Uppsala, 14:00
Available from: 2003-04-29 Created: 2003-04-29Bibliographically approved

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