Caimi Karina, Cataldi Angel
Instituto de Biotecnología, CICVyA/INTA, Los Reseros y Las Cabañas, Castelar 1712, Argentina.
Comp Funct Genomics. 2004;5(2):116-22. doi: 10.1002/cfg.380.
The direct repeat (DR) region is a singular locus of the Mycobacterium tuberculosis 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 M. smegmatis, M. avium, M. marinum and M. leprae genomes contain sequences and ORFs similar to those of the DR locus of the M. tuberculosis complex, we analysed the corresponding regions in these species. As a first step, some conserved genes that flank the DR genes [Rv2785c (rpsO), Rv2786c (ribF), Rv2790c (ltp1 ), Rv2793c (truB), Rv2800, Rv2825, Rv2828, Rv2831 (echA16 ), Rv2838 (rbfA) and Rv2845 (proS )] were used as markers to locate the corresponding orthologues in M. smegmatis, M. avium, M. marinum and M. leprae in silico. Most of these M. tuberculosis 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 Rv2801-Rv2824, suggesting that these genes are unique to M. tuberculosis within the genus Mycobacterium.We observed that in M. smegmatis and M. avium, Rv2800 and Rv2825 are adjacent. This observation was experimentally confirmed by PCR. In conclusion, as the DR locus and the ORFs around it are absent in M. smegmatis and M. avium and, as it is possible that these species are older than M. tuberculosis, we postulated that the DR locus was acquired by the M. tuberculosis complex species or by an ancestor bacterium.
直接重复（DR）区域是结核分枝杆菌复合群基因组的一个独特位点。该区域由36 bp的重复序列组成，这些重复序列被非重复的独特间隔序列隔开。在这个区域周围有几个编码功能未知蛋白质的基因。为了确定耻垢分枝杆菌、鸟分枝杆菌、海分枝杆菌和麻风分枝杆菌的基因组是否包含与结核分枝杆菌复合群DR位点相似的序列和开放阅读框（ORF），我们分析了这些物种的相应区域。第一步，我们使用DR基因侧翼的一些保守基因[Rv2785c（rpsO）、Rv2786c（ribF）、Rv2790c（ltp1）、Rv2793c（truB）、Rv2800、Rv2825、Rv2828、Rv2831（echA16）、Rv2838（rbfA）和Rv2845（proS）]作为标记，在计算机上定位耻垢分枝杆菌、鸟分枝杆菌、海分枝杆菌和麻风分枝杆菌中的相应直系同源基因。这些结核分枝杆菌标记基因中的大多数在其他分枝杆菌中都有高度相似的直系同源基因，且排列顺序和方向相同。相比之下，未发现ORF Rv2801 - Rv2824的直系同源基因，这表明这些基因在分枝杆菌属中是结核分枝杆菌所特有的。我们观察到，在耻垢分枝杆菌和鸟分枝杆菌中，Rv2800和Rv2825是相邻的。这一观察结果通过PCR得到了实验证实。总之，由于耻垢分枝杆菌和鸟分枝杆菌中不存在DR位点及其周围的ORF，并且由于这些物种可能比结核分枝杆菌更古老，我们推测DR位点是由结核分枝杆菌复合群物种或其祖先细菌获得的。
