Mu transposase-stimulated illegitimate recombination of Tn3kan- and IS101-containing plasmids.

The transposable bacteriophage Mu and the mobile genetic elements Tn3 and IS101 replicatively transpose to random target sites, produce 5 bp target site duplications, and contain the sequence 5'-PuCGAAAPu-3' starting at bp 21 from their ends. The presence of these shared characteristics, plus the fact that Mu transposase can specifically bind to the termini of Tn3 and IS101 in vitro, suggests that the elements may be evolutionarily conserved and retain some functional capacity to transpose each other's DNA. To examine this proposition, in vivo transposition-mating assays were performed and demonstrated that Mu transposase stimulated the formation of recA-independent recombination products between Tn3kan- or IS101-containing plasmids and a target plasmid (pOX38cam) up to 200-fold. However, when transferred to recA+ hosts, these recA-independent products yielded resolution products suggestive of illegitimate recombination, as similar recombination and resolution products were generated, at reduced frequencies, in the absence of Mu transposase. Thus, Mu transposase may stimulate a host-mediated, recA-independent illegitimate recombination reaction. As adjacent pSC101 sequences, including a formerly unknown but functional IHF site (bp 2238-2251), were required for Mu transposase-stimulated IS101 illegitimate recombination, IHF may be one of the putative host factors involved in these recombination reactions.