<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 direct repeat (DR) region is a singular locus of the <italic>Mycobacterium tuberculosis</italic>
complex genome. This region consists of 36 bp repetitive sequences separated by
non-repetitive unique spacer sequences. Around this region there are several genes
coding for proteins of unknown function. To determine whether the <italic>M. smegmatis, M.
avium, M. marinum</italic> and <italic>M. leprae</italic> genomes contain sequences and ORFs similar to
those of the DR locus of the <italic>M. tuberculosis</italic> complex, we analysed the corresponding
regions in these species. As a first step, some conserved genes that flank the DR genes
[<italic>Rv2785c (rpsO), Rv2786c (ribF), Rv2790c (ltp1 ), Rv2793c (truB), Rv2800, Rv2825,
Rv2828, Rv2831 (echA16 ), Rv2838 (rbfA)</italic> and <italic>Rv2845 (proS )</italic>] were used as markers
to locate the corresponding orthologues in <italic>M. smegmatis, M. avium, M. marinum</italic> and
<italic>M. leprae in silico</italic>. Most of these <italic>M. tuberculosis</italic> marker genes have highly similar
orthologues located in the same order and orientation in the other mycobacteria. In
contrast, no orthologues were found for ORFs <italic>Rv2801–Rv2824</italic>, suggesting that these
genes are unique to <italic>M. tuberculosis</italic> within the genus <italic>Mycobacterium</italic>.We observed that
in <italic>M. smegmatis</italic> and <italic>M. avium, Rv2800</italic> and <italic>Rv2825</italic> are adjacent.
This observation was experimentally confirmed by PCR. In conclusion, as the DR locus and the ORFs
around it are absent in <italic>M. smegmatis</italic> and <italic>M. avium</italic> and, as it is possible that these
species are older than <italic>M. tuberculosis</italic>, we postulated that the DR locus was acquired
by the <italic>M. tuberculosis</italic> complex species or by an ancestor bacterium.</p>
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Comp Funct Genomics. 2004 Mar; 5(2):116-122