Site-specific recombination between plasmids of Staphylococcus aureus.

Anomalous recombination between two similar but nonidentical, naturally occurring penicillinase plasmids, pI258 and pI524, leading to duplication and deletion of the beta-lactamase locus, is described. Physical mapping of these plasmids by heteroduplex and restriction analysis revealed that the beta-lactamase loci were homologous and in inverted orientation with respect to one another and that their respective locations were separated by a short region of homology. This intervening region of homology included one copy of a segment that was repeated on pI524 in inverted orientation at a distance of 2.2 kilobase pairs and contained a recognition sequence for a site-specific, rec-independent recombination function that caused reversible inversion of this segment on pI524. It is proposed that site-specific, intermolecular recombination involving this repeated sequence was responsible for the observed results.