Tn552 transposase catalyzes concerted strand transfer in vitro

The Tn552 transposase, a member of the DDE superfamily of transposase and retroviral integrase proteins, has been expressed in soluble form. The purified protein performs concerted strand transfer in vitro, efficiently pairing two preprocessed transposon ends and inserting them into target DNA. For maximum efficiency, both participating DNA ends must contain the two adjacent transposase-binding sites that are the normal constituents of the Tn552 termini. As is the case with transposition in vivo, the insertions recovered from the reaction in vitro are flanked by repeats of a short target sequence, most frequently 6 bp. The reaction has stringent requirements for a divalent metal ion. Concerted strand transfer is most efficient with Mg2+. Although it stimulates strand transfer overall, Mn2+ promotes uncoupled, single-ended events at the expense of concerted insertions. The simplicity and efficiency of the Tn552 transposition system make it an attractive subject for structural and biochemical studies and a potentially useful genetic tool.

Arrayed transposase-binding sequences on the ends of transposon Tn5090/Tn402

The transposon Tn5090/Tn402 encodes a 559 amino acid transposase, TniA, with a DDE motif. Gel mobility shifting and cleavage protection analysis with DNase I and hydroxyl radical probes revealed that TniA binds to multiple repeat sequences on either terminus of Tn5090/Tn402. Four of these TniA-binding 19mers occurred on the left-hand (t) end and two on the right-hand (i) end. Hydroxyl radical cleavage protection demonstrated the presence of 3–6 bp contact sequences on one face of the DNA helix. The binding pattern and organisation of repeats suggested parallels between Tn5090/Tn402 and Mu, which controls its transpositional activity in the assembly step of a higher order transpososome complex. The complex terminal structure and genes of transposase and nucleotide-binding proteins in tandem are hallmarks of the handful of Mu-like elements that are known to date.