REARRANGEMENTS IN THE STAPHYLOCOCCAL BETA-LACTAMASE-ENCODING PLASMID,PIP1066, INCLUDING A DNA INVERSION THAT GENERATES 2 ALTERNATIVE TRANSPOSONS

The plasmid pIP1066, harboured by a methicillin-resistant Staphylococc us aureus strain isolated in France, carries genes specifying beta-lac tamase. This plasmid undergoes numerous rearrangements. One of these w as an insertion, between the genes binR and sin encoding resolvases, o f a 16 kb element which displayed the characteristic features of a tra nsposon. This putative transposon, named Tn5404, carried genes encodin g proteins involved in its transposition, as well as a resolution syst em, which were indistinguishable from those of the S. aureus transposo n Tn552. These were: p480 encoding a probable transposase, p271 encodi ng a putative ATP-binding protein, binL encoding a resolvase, and a re solution site, rest. In addition, Tn5404 carried aminoglycoside-resist ance genes (aphA, str) and the insertion sequence IS1181. Tn5404 conta ined at its termini 116 bp imperfect inverted repeats, similar to thos e of Tn552, and was flanked by 6 bp direct repeats. Insertion of Tn540 4 close to resR and to the structural and regulatory beta-lactamase ge nes (blaZ, blaI, blaR1) of pIP1066, generated a 3.5kb invertible segme nt flanked by inversely repeated resolution sites (resR, resL). This i nvertible segment, which carried p480, p271 and binL, generated Tn552 or Tn5404 depending on its orientation. Thus, these two transposons sh are their transposition and resolution systems.