Par site of the ColN plasmid: structural and functional organization.

A par site involved in the resolution of multimeric plasmid DNA forms was localized in a 679 bp SalI-KpnI fragment of the small colicinogenic plasmid ColN. It was shown that replication of the monomeric pUC19 recombinant plasmid carrying the par region of ColN does not result in the formation of significant numbers of multimers. In order to function properly, the ColN multimer resolution mechanism requires the product of the xerA gene, just as in the case of ColE1. Nucleotide sequence analysis of the par region of ColN revealed substantial homology with the par locus of the ColE1 plasmid. The results of this study and data from the literature indicate that the par sites of ColE1-type plasmids have substantial homology and the same mechanism of action, and in fact represent a universal stability module for small multicopy colicinogenic plasmids.