Mini-P1 plasmid partitioning: excess ParB protein destabilizes plasmids containing the centromere parS

Author:

Funnell B E1

Affiliation:

1. Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20892.

Abstract

The partition system of the unit-copy plasmid P1 consists of two proteins, the parA and parB gene products, and a cis-acting site, parS. Production of high levels of the P1 ParB protein, from an external promoter on a high-copy-number vector, inhibits the propagation of lambda-mini-P1 prophages and destabilizes other P1-derived plasmids. The interference by ParB protein depends on the parS site, or centromere, of the P1 partition region; plasmids lacking parS are unaffected. The defect is more severe than the defect due to mutations that simply eliminate par function. In the presence of excess ParB protein, plasmids carrying parS are more unstable than would be predicted from a random distribution at cell division. The destabilization is a segregation defect, as the copy number of parS-bearing plasmids is not decreased under these conditions. Thus, it appears that ParB protein binds to parS; if too much protein is present, it sequesters such plasmids so they cannot be properly, or even randomly, partitioned. This suggests that under normal conditions, ParB protein recognizes and binds to parS and may be the protein responsible for pairing plasmids during the process of partitioning at cell division.

Publisher

American Society for Microbiology

Subject

Molecular Biology,Microbiology

Reference29 articles.

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2. Partition of unit-copy miniplasmid to daughter cells. I. P1 and F miniplasmids contain discrete, interchangeable sequences sufficient to promote equipartition;Austin S.;J. Mol. Biol.,1983

3. Partition of unit-copy miniplasmids to daughter cells. II. The partition region of miniplasmid P1 encodes an essential protein and a centromere-like site at which it acts;Austin S.;J. Mol. Biol.,1983

4. Austin S. and A. Abeles. 1985. The partition functions of P1 P7 and F miniplasmids p. 215-226. In D. R. Helinski S. N. Cohen D. B. Clewell D. A. Jackson and A. Hollaender (ed.) Plasmids in bacteria. Plenum Publishing Corp. New York.

5. Genetic and physical map of a P1 miniplasmid;Austin S.;J. Bacteriol.,1982

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