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Journal of Bacteriology, January 2004, p. 207-211, Vol. 186, No. 1
0021-9193/04/$08.00+0 DOI: 10.1128/JB.186.1.207-211.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
and Kurt Nordström*
Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, S-751 24 Uppsala, Sweden
Received 31 March 2003/ Accepted 1 October 2003
Plasmid R1 is a low-copy-number plasmid that is present at a level of about four or five copies per average cell. The copy number is controlled posttranscriptionally at the level of synthesis of the rate-limiting initiator protein RepA. In addition to this, R1 has an auxiliary system that derepresses a second promoter at low copy numbers, leading to increased repA mRNA synthesis. This promoter is normally switched off by a constitutively synthesized plasmid-encoded repressor protein, CopB; in cells with low copy numbers, the concentration of CopB is low and the promoter is derepressed. Here we show that the rate of loss of a Par+ derivative of the basic replicon of R1 increased about sevenfold when the cells contained a high concentration of the CopB protein formed from a compatible plasmid.
Present address: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.
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