Interaction of Related Tn 916 -Like Transposons: Analysis of Excision Events Promoted by Tn 916 and Tn 5386 Integrases

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Abstract
In recent work, we described the excision of a large genomic region from Enterococcus faecium D344R in which the sequence from “joint” regions suggested that excision resulted from the interaction of conjugative transposon Tn 916 and the related mobile element Tn 5386 . In the present study, we examined the ability of integrases and integrase-excisase combinations from Tn 916 and Tn 5386 to promote the excision of constructs consisting of the termini of Tn 916 , Tn 5386 , and the VanB mobile element Tn 5382 . Integrases alone from either Tn 916 or Tn 5386 promoted the circularization of constructs from the three different transposons, even when the different termini used in the constructs were discordant in their transposon of origin. The termini of Tn 916 and Tn 5382 found in all joints were consistent with previously identified Tn 916 and Tn 5382 termini. Substantial variation was seen in the integrase terminus of Tn 5386 used to form joints, regardless of the integrase that was responsible for circularization. Variability was observed in joints formed from Tn 5386 constructs, in contrast to joints observed with the termini of Tn 916 or Tn 5382 . The coexpression of excisase yielded some variability in the joint regions observed. These data confirm that integrases from some Tn 916 -like elements can promote circularization with termini derived from heterologous transposons and, as such, could promote excision of large genomic regions flanked by such elements. These findings also raise interesting questions about the sequence specificities of the C terminals of Tn 916 -like integrases, which bind to the ends and facilitate strand exchange.