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We have previously shown that the methicillin-resistance gene mecA of Staphylococcus aureus strain N315 is localized within a large (52-kb) DNA cassette (designated the staphylococcal cassette chromosome mec SCCmec) inserted in the chromosome. By sequence determination of the entire DNA, we identified two novel genes (designated cassette chromosome recombinase genes ccrA and ccrB) encoding polypeptides having a partial homology to recombinases of the invertase/resolvase family. The open reading frames were found to catalyze precise excision of the SCCmec from the methicillin-resistant S. aureus chromosome and site-specific as well as orientation-specific integration of the SCCmec into the S. aureus chromosome when introduced into the cells as a recombinant multicopy plasmid. We propose that SCCmec driven by a novel set of recombinases represents a new family of staphylococcal genomic elements.
Katayama et al. (Thu,) studied this question.