<p>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.</p><p>In my thesis, I have studied control of chromosome and plasmid replication in <i>Escherichia coli</i>, a rod-shaped bacterium. Plasmids are extrachromosomal autonomously replicating DNA molecules. </p><p>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.</p><p>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.</p><p>Fast-growing <i>E. coli</i> has overlapping replicative phases with synchronous initiation from multiple initiation sites, <i>oriC</i>. 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.</p><p>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.</p><p>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 +<i>n</i> model.</p><p>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.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-3471 |
| Date | January 2003 |
| Creators | Olsson, Jan |
| Publisher | Uppsala University, Department of Cell and Molecular Biology, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 838 |
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