Inducible transposition in Streptomyces lividans of insertion sequence IS6100 from Mycobacterium fortuitum

Transposition of IS6100, originally isolated as part of the compound transposon Tn610 from Mycobacterium fortuitum, was tested in the related actinomycete Streptomyces lividans. Cointegrate formation was observed, as expected for this IS6-related element, and involved apparent random integration of the temperature-sensitive vector carrying IS6100 and concomitant duplication of the insertion sequence. This establishes that a single copy of the insertion sequence can promote transposition and is a precedent for the functioning of a heterologous transposable element in Streptomyces. Transposition could be induced 100-fold by external transcription emanating from a copy of the thiostrepton-inducible promoter ptipA located outwith the insertion sequence and resulting in overexpression of the transposase gene. Thus, in contrast to other prokaryotic transposable elements, IS6100 appears to have no effective means of protecting itself from external activation.