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Journal of Bacteriology, September 2002, p. 4857-4867, Vol. 184, No. 17
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.17.4857-4867.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Effects of the P1 Plasmid Centromere on Expression of P1 Partition Genes

Jian-Jiang Hao^, and Michael Yarmolinsky^*

Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255

Received 25 March 2002/ Accepted 5 May 2002

The partition operon of P1 plasmid encodes two proteins, ParA and ParB, required for the faithful segregation of plasmid copies to daughter cells. The operon is followed by a centromere analog, parS, at which ParB binds. ParA, a weak ATPase, represses the par promoter most effectively in its ADP-bound form. ParB can recruit ParA to parS, stimulate its ATPase, and significantly stimulate the repression. We report here that parS also participates in the regulation of expression of the par genes. A single chromosomal parS was shown to augment repression of several copies of the par promoter by severalfold. The repression increase was sensitive to the levels of ParA and ParB and to their ratio. The increase may be attributable to a conformational change in ParA mediated by the parS-ParB complex, possibly acting catalytically. We also observed an in cis effect of parS which enhanced expression of parB, presumably due to a selective modulation of the mRNA level. Although ParB had been earlier found to spread into and silence genes flanking parS, silencing of the par operon by ParB spreading was not significant. Based upon analogies between partitioning and septum placement, we speculate that the regulatory switch controlled by the parS-ParB complex might be essential for partitioning itself.

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* Corresponding author. Mailing address: Laboratory of Biochemistry, National Cancer Institute, NIH, 37 Convent Dr., Bethesda, MD 20892-4255. Phone: (301) 496-5226. Fax: (301) 402-3095. E-mail: myarmo{at}helix.nih.gov.

Present address: Department of Experimental Pathology, Holland Laboratory, American Red Cross, Rockville, MD 20855.

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Journal of Bacteriology, September 2002, p. 4857-4867, Vol. 184, No. 17
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.17.4857-4867.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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