Features of the replicon of plasmid pAM10.6 of Pseudomonas fluorescens

We describe features of the basic replicon of the 10.6-kb medium-copy-number plasmid pAM10.6. pAM10.6 was able to replicate in various Pseudomonas strains but was maintained in Escherichia coli only after the p15A origin of replication was inserted. Deletion analysis suggests that the pAM10.6 origin of replication is located in a 0.5-kb region that includes inverted and direct repeats upstream of the repA gene. RepA (204 aa) has a clear homology to plasmid replication proteins of some other gram-negative bacteria. The pas (plasmid addiction system) (genes encoded in the region of 480-bp) stabilizes plasmid maintenance in P. putida cells under nonselective conditions for at least 200 generations. A 3.75-kb PstI fragment of pAM10.6 joined to a Km(r) gene was shown to be a minimal plasmid unit maintained in P. putida as a monomer. Further deletions of this 3.75-kb fragment caused a drive to form stable head-to-tail dimeric plasmids in P. putida.