Tn5053, a mercury resistance transposon with integron's ends

We describe a novel type of mercury resistance transposon, Tn5053, which was found in the chromosome of a mercury-resistant Xanthomonas strain isolated from a mercury mine. An 8400 base-pair Tn5053 is bracketed by 25 base-pair inverted repeats that have no sequence homology with inverted repeats of classical mercury resistance transposons Tn501 and Tn21. Instead they show high homology with inverted repeats bracketing the antibiotic resistance segment of Tn21 (integron In2). A 38 base-pair element, which is highly homologous to the inverted repeats of classical mercury resistance transposons has been found within Tn5053 near one of its ends. This internal inverted repeat is fused to the mer operon of Tn5053 in exactly the same way as in the Tn501 mercury resistance transposon. This finding suggests that the mer operon was integrated into the Tn5053 transposition module not through integron-specific pathway but rather via insertion of a classical mercury resistance transposon.