MOBILE GENETIC ELEMENTS IN MYCOBACTERIA

Mobile genetic elements, ranging from plasmids and bacteriophages to i nsertion sequences and transposons, have come to play key roles in man y aspects of basic and applied research in mycobacteriology, Plasmids and bacteriophages have been widely used as cloning vectors, especiall y for constructing recombinant vaccines based on bacille Calmette-Guer in (BCG); composite transposons have also been used for this purpose, At the same time, insertion sequences have proved invaluable for diagn ostic and epidemiological studies, and transposon mutagenesis provides a useful method for inactivating and marking selected mycobacterial g enes. Plasmids are commonly found in many mycobacterial species, notab ly M. avium, although not in M. tuberculosis; the biological significa nce of these plasmids (if any) is mostly unknown, Insertion sequences, and other repetitive elements, have also been characterized from many mycobacterial species, Special attention is paid to IS6110/IS986, fro m M. tuberculosis, and the IS900 family from M. avium and related orga nisms; the latter includes the recently described highly mobile elemen t IS1110. The emphasis of the paper is on the molecular biology and si gnificance of plasmids and insertion sequences/transposons, in mycobac teria and in bacteria in general, and their applications as cloning ve ctors and in transposon mutagenesis.