<p>This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.</p> <p>The <italic>Mycobacterium tuberculosis</italic> complex is associated with a remarkably low level of structural gene polymorphism. As part of a search for alternative forms of genetic variation that may act as a source of biological diversity in <italic>M. tuberculosis</italic>, we have identified a region of the genome that is highly variable amongst a panel of unrelated clinical isolates. Fifteen of 24 isolates examined contained one or more copies of the <italic>M. tuberculosis</italic>-specific IS<italic>6110</italic> insertion element within this 20 kb variable region. In nine of the isolates, including the laboratory-passaged strain H37Rv, genomic deletions were identified, resulting in loss of between two and 13 genes. In each case, deletions were associated with the presence of a copy of the IS<italic>6110</italic> element. Absence of flanking tri- or tetra-nucleotide repeats identified homologous recombination between adjacent IS<italic>6110</italic> elements as the most likely mechanism of the deletion events. IS<italic>6110</italic> insertion into hot-spots within the genome of <italic>M. tuberculosis</italic> provides a mechanism for generation of genetic diversity involving a high frequency of insertions and deletions.</p>
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Yeast. 2000; 17(4):272-282