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. 1986 May;83(10):3116–3120. doi: 10.1073/pnas.83.10.3116

Unique type of plasmid maintenance function: postsegregational killing of plasmid-free cells.

K Gerdes, P B Rasmussen, S Molin
PMCID: PMC323463  PMID: 3517851

Abstract

The stability locus parB+ of plasmid R1 has been found to specify a unique type of plasmid maintenance function. Two genes, hok (host killing) and sok (suppressor of killing), are required for the stabilizing activity. The hok gene encodes a highly toxic gene product, whose overexpression causes a rapid killing and a concomitant dramatic change in morphology of the host cell. The other gene, sok, was found to encode a product that counteracts the hok gene-mediated killing. The parB+ region was inserted in a plasmid with a temperature-sensitive replication system. At nonpermissive temperature, the parB+ plasmid was maintained in the population for a significantly longer period than the corresponding parB- plasmid. Coupled to this extended maintenance, a large fraction of the population was shown to be nonviable plasmid-free cells with the characteristic hok-induced change in morphology. Based on these findings, we propose that the parB+ locus mediates plasmid stability by killing cells that have lost the parB+ plasmid during the preceding cell division, thereby ensuring that a growing bacterial culture predominantly consists of plasmid-containing cells.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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