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Mechanizmy stabilnego dziedziczenia plazmidów

100%

Zielenkiewicz U. , Cegłowski P.

nr 3

297-304

Summary The stable inheritance of bacterial plasmids is achieved by a number of different mechanisms. Among them are: resolution of plasmid multimers into monomers, selective killing of plasmid-free segregants and active plasmid partitioning into dividing cells. The first two mechanisms are discussed in this article. The multimer resolution systems (mrs) consist of a site specific recombinase (resolvase) and the defined nucleotide sequence res located on the plasmid. By specific recombination between repeated res sequences the recombinase resolves plasmid oligomers to monomers. This maximizes the number of plasmid units prior to cell division and considerably contributes to stable maintenance of plasmid in bacterial cells. The post-segregational killing systems involve a stable poison and an unstable antidote. The antidotes nautralize their cognate poisons or prevent their synthesis. The different decay rates of the poisons and the antidotes underlie the molecular mechanisms of poison activation in plasmid-free cells. By killing and eliminating plasmid-free cells from the population of plasmidbearing ones the poison-antidote couples act therefore as plasmid addiction systems. While the mrs maximize the random plasmid distribution into the dividing cells addiction systems assure better-than-random plasmid distribution.

Characterization of Bacillus subtilis clones surviving overproduction of Zeta, a pSM19035 plasmid-encoded toxin.

80%

Nowakowska B. , Kern-Zdanowicz I. , Zielenkiewicz U. , Cegłowski P.

2005

tom 52

nr 1

99-107

The postsegregational killing system of pSM19035 plasmid consists of the proteins Zeta and Epsilon, a toxin and an antidote, respectively. Zeta mutants were isolated with the use of Bacillus subtilis strain with the ζ gene under control of an inducible promoter integrated into the chromosome. Results of mutant analysis point to the amino terminal part of the Zeta protein as being responsible for the toxicity.