Specificity switching of the P1 plasmid centromere-like site.

The P1 plasmid partition site acts like a centromere, promoting accurate segregation of copies to daughter cells. A 34 bp segment is essential for partition and binds the plasmid ParB protein. Additional sequences act as specificity elements that direct the choice of copies for partition. They include a second ParB binding site and a site for the host integration host factor protein. Sites lacking one or more of these additional elements are switched to a different specificity. Defined mutants were scored for partition specificity and protein binding. The results suggest that the wild-type site is folded in a specific DNA-protein complex. Disruption of the complex leads to an open configuration which, while still active in partition, has altered recognition specificity.