Sites for co-integration of large staphylococcal plasmids.

Site-specific recombination is thought to play an important role in the evolution of multi-resistant plasmids in bacteria, including the human pathogen Staphylococcus aureus (Sa). A mechanism for site- and orientation-specific recombination between large Sa plasmids was identified in Sa strain 1054. A replication-thermosensitive derivative of plasmid pI9789::Tn552 (called pS1) was found to form stable co-integrates with the large plasmid pOX1054 in the Sa strain 1054. Two closely related recombination sites were identified on these plasmids at which recombination occurred to form co-integrates. The sites (rs9789 from plasmid pI9789::Tn552 and rs1054 from pOX1054) were cloned and studies with them showed that the recombination at these sites occurs by a new method. The site rs1054 (27 bp) is deleted and rs9789 (26 bp) is duplicated during recombination. The data show that plasmid pS1 contributes the site for recombination and that the gene(s) encoding the protein(s) involved in recombination are encoded on either pOX1054 or the 1054 chromosome.