Characterization of IS1547, a new member of the IS900 family in the Mycobacterium tuberculosis complex, and its association with IS6110

Unlike classically defined insertion sequence (IS) elements, which are deli mited by their inverted terminal repeats, some IS elements do not have inve rted terminal repeats. Among this group of atypical IS elements, IS116, IS9 00, IS901, and IS1110 have been proposed as members of the IS900 family of elements, not only because they do not have inverted terminal repeats but a lso because they share other features such as homologous transposases and p articular insertion sites. In this study, we report a newly identified IS s equence, IS1547, which was first identified in a clinical isolate of Mycoba cterium tuberculosis. Its structure, insertion site, and putative transposa se all conform with the conventions of the IS900 family, suggesting that it is a new member of this family. IS1547 was detected only in isolates of th e M. tuberculosis complex, where it had highly polymorphic restriction frag ment length polymorphism patterns, suggesting that it may be a useful genet ic marker for identifying isolates of the M. tuberculosis complex and for d istinguishing different strains of M. tuberculosis. ipl is a preferential l ocus for IS6110 insertion where there are eight known different insertion s ites for IS6110. Surprisingly, the DNA sequence of ipl is now known to be a part of IS1547, meaning that IS1547 is a preferential site for IS6110 inse rtion.