IDENTIFICATION AND CHARACTERIZATION OF GENES INVOLVED IN EXCISION OF THE LACTOCOCCUS-LACTIS CONJUGATIVE TRANSPOSON TN5276

The 70-kb transposon Tn5276, originally detected in Lactococcus lactis NIZO R5 and carrying the genes for nisin production and sucrose ferme ntation, can be conjugally transferred to other L. lactis strains. Seq uence analysis and complementation studies showed that the right end o f Tn5276 contains two genes, designated xis and int, which are involve d in excision. The 379-amino-acid int gene product shows high (up to 5 0%) similarity with various integrases, including that of the Tn916-re lated conjugative transposons. The xis gene product, like almost all k nown excisionase (Xis) proteins, is a small (68-residue), basic protei n. Expression of both the Tn5276 int and xis genes is required for eff icient excision of the ends of Tn5276 in Escherichia coil that appeare d to be circularized in the excision process. Mutational analysis of t he xis and int genes showed that excision efficiency is dependent on t he integrity of the int gene but that an intact xis gene is also requi red for efficient excision.