Context-sensitive transposition of IS6110 in mycobacteria

The rational use of IS6110 fingerprinting for studies of the molecular epid emiology and evolution of Mycobacterium tuberculosis requires understanding of the dynamics of transposition. In laboratory model systems, it has been shown that transposition is context-sensitive, i.e. it is influenced by th e nature of the site in which the insertion sequence is presented. Stimulat ion of transposition by activation of an adjacent promoter supports the hyp othesis that transposition occurs more readily from transcriptionally activ e locations. In addition, it has been shown that transposition can be enhan ced by the expression of the transposase in trans. These findings imply tha t the frequency of transposition will vary substantially between different strains of M. tuberculosis, and furthermore that a hitherto stable strain m ay develop more rapid variation due to transposition into an active site. T he use of IS6110 fingerprinting for the analysis of longer-range relationsh ips between M. tuberculosis isolates therefore needs to be interpreted with care.