Movement of IS26-associated antibiotic resistance genes occurs via a translocatable unit that includes a single IS26 and preferentially inserts adjacent to another IS26.
Bottom Line: Intact transposase genes in both IS26s were required for high-frequency cointegrate formation as inactivation of either one reduced the frequency 30-fold.Conversion of each residue in the DDE motif of the Tnp26 transposase also reduced the cointegration frequency.IS26-flanked structures deceptively resemble class I transposons, but this work reveals that the features of IS26 movement do not resemble those of the IS and class I transposons studied to date.
Affiliation: School of Molecular Bioscience, The University of Sydney, Sydney, Australia.Show MeSH
Related in: MedlinePlus
Mentions: Antibiotic resistance genes flanked by IS26s resemble class I or composite transposons, which consist of two ISs flanking a central segment. In most cases, the IS26s are in a direct orientation. However, structures containing more than two IS26s exhibit a feature that is not consistent with this designation because they include multiple putative composite transposons (IS26-unique segment-IS26) in an array that contains too few copies of the IS (11). That is, the adjacent putative transposons share a single IS26 located between them. An example of two overlapping IS26-bounded structures, each of which is also found alone, has been found in several locations (11). Further examples of these arrays are found in many complex regions containing several different antibiotic resistance genes (for examples, see references 11, 15, and 23–25). The arrangement is shown schematically in Fig. 1A. This configuration cannot be explained if the individual “transposons” move in the same way as the well-studied composite transposons Tn5 and Tn10 (26, 27), which move as a single discrete unit. Duplication of IS26-flanked structures detected after the selective pressure of antibiotic use has also been reported, and this leads to the formation of tandem arrays (Fig. 1B) of the same DNA fragment interspersed with directly oriented copies of IS26 (28–31).
Affiliation: School of Molecular Bioscience, The University of Sydney, Sydney, Australia.