REPLICATION OF THE PROMISCUOUS PLASMID PLS1 - A REGION ENCOMPASSING THE MINUS ORIGIN OF REPLICATION IS ASSOCIATED WITH STABLE PLASMID INHERITANCE

Deletion of a region of the promiscuous plasmid pLS1 encompassing the initiation signals for the synthesis of the plasmid lagging strand led to plasmid instability in Streptococcus pneumoniae and Bacillus subti lis. This defect could not be alleviated by increasing the number of c opies (measured as double-stranded plasmid DNA) to levels similar to t hose of the wild-type plasmid pLS1. Our results indicate that in the v icinity of, or associated with the single-stranded origin region of pL S1 there is a plasmid component involved in its stable inheritance. Ho mology was found between the DNA gyrase binding site within the par re gion of plasmid pSC101 and the pLS1 specific recombination site RS(B).