The large resolvase TndX is required and sufficient for integration and excision of derivatives of the novel conjugative transposon Tn5397.

Tn5397 is a novel conjugative transposon, originally isolated from Clostridium difficile. This element can transfer between C. difficile strains and to and from Bacillus subtilis. It encodes a conjugation system that is very similar to that of Tn916. However, insertion and excision of Tn5397 appears to be dependent on the product of the element encoded gene tndX, a member of the large resolvase family of site-specific recombinases. To test the role of tndX, the gene was cloned and the protein was expressed in Escherichia coli. The ability of TndX to catalyze the insertion and excision of derivatives (minitransposons) of Tn5397 representing the putative circular and integrated forms, respectively, was investigated. TndX was required for both insertion and excision. Mutagenesis studies showed that some of the highly conserved amino acids at the N-terminal resolvase domain and the C-terminal nonconserved region of TndX are essential for activity. Analysis of the target site choices showed that the cloned Tn5397 targets from C. difficile and B. subtilis were still hot spots for the minitransposon insertion in E. coli.