Site-specific recombination between plasmids of Staphylococcus aureus

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Naturally occurring penicillinase plasmids, such as pI258 and pI524, can undergo recombination.
• Understanding plasmid recombination is crucial for antibiotic resistance gene dissemination.

Purpose of the Study:

• To investigate the mechanism of anomalous recombination between plasmids pI258 and pI524.
• To elucidate the role of homologous regions and specific DNA sequences in this recombination event.

Main Methods:

• Physical mapping of plasmids using heteroduplex analysis.
• Restriction enzyme digestion and analysis.
• Sequence analysis to identify homologous regions and recognition sites.

Main Results:

• Plasmids pI258 and pI524 share homologous beta-lactamase loci in an inverted orientation.
• A short region of homology between the plasmids contains a repeated DNA segment.
• This segment is recognized by a site-specific, rec-independent recombination function, causing its inversion.

Conclusions:

• Site-specific, intermolecular recombination involving the repeated sequence is proposed as the cause of anomalous recombination.
• This recombination event led to duplication and deletion of the beta-lactamase locus.
• The findings highlight a novel mechanism for genetic instability in plasmids.