A site-specific recombination function in Staphylococcus aureus plasmids

All known small staphylococcal plamids possess one or two recombination sites at which site-specific cointegrate formation occur. One of these sites, RS(A), is present on two small multicopy plasmids, pT181 and pE194; it consists of 24 base pairs of identity in the two plasmids, the 'core,' flanked by some 50 pairs of decreasing homology. Here we show that recombination at RS(A) is recA independent and is mediated by a plasmid-encoded, trans-acting protein, Pre (plasmid recombination). Pdre-mediated recombination is site specific in that it occurs within the core seqence of RS(A) in a recA1 host. Recombination also occurs between two intramolecular RS(A) sites. Unlike site-specific recombination systems encoded by other plasmids, Pre-RS(A) is not involved in plasmid maintenance.