Brooks P C, Movahedzadeh F, Davis E O
Division of Mycobacterial Research, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, England.
J Bacteriol. 2001 Aug;183(15):4459-67. doi: 10.1128/JB.183.15.4459-4467.2001.
The repair of DNA damage is expected to be particularly important to intracellular pathogens such as Mycobacterium tuberculosis, and so it is of interest to examine the response of M. tuberculosis to DNA damage. The expression of recA, a key component in DNA repair and recombination, is induced by DNA damage in M. tuberculosis. In this study, we have analyzed the expression following DNA damage in M. tuberculosis of a number of other genes which are DNA damage inducible in Escherichia coli. While many of these genes were also induced by DNA damage in M. tuberculosis, some were not. In addition, one gene (ruvC) which is not induced by DNA damage in E. coli was induced in M. tuberculosis, a result likely linked to its different transcriptional arrangement in M. tuberculosis. We also searched the sequences upstream of the genes being studied for the mycobacterial SOS box (the binding site for LexA) and assessed LexA binding to potential sites identified. LexA is the repressor protein responsible for regulating expression of these SOS genes in E. coli. However, two of the genes which were DNA damage inducible in M. tuberculosis did not have identifiable sites to which LexA bound. The absence of binding sites for LexA upstream of these genes was confirmed by analysis of LexA binding to overlapping DNA fragments covering a region from 500 bp upstream of the coding sequence to 100 bp within it. Therefore, it appears most likely that an alternative mechanism of gene regulation in response to DNA damage exists in M. tuberculosis.
DNA损伤修复对于诸如结核分枝杆菌这样的细胞内病原体而言预计尤为重要，因此研究结核分枝杆菌对DNA损伤的反应很有意义。recA是DNA修复和重组中的关键成分，其表达在结核分枝杆菌中受DNA损伤诱导。在本研究中，我们分析了结核分枝杆菌中一些在大肠杆菌中受DNA损伤诱导的其他基因在DNA损伤后的表达情况。虽然这些基因中的许多在结核分枝杆菌中也受DNA损伤诱导，但有些则不然。此外，一个在大肠杆菌中不受DNA损伤诱导的基因（ruvC）在结核分枝杆菌中被诱导，这一结果可能与其在结核分枝杆菌中不同的转录排列有关。我们还在被研究基因的上游序列中搜索了分枝杆菌SOS框（LexA的结合位点），并评估了LexA与所鉴定潜在位点的结合情况。LexA是负责调节大肠杆菌中这些SOS基因表达的阻遏蛋白。然而，在结核分枝杆菌中受DNA损伤诱导的两个基因没有可识别的LexA结合位点。通过分析LexA与覆盖从编码序列上游500 bp到其内部100 bp区域的重叠DNA片段的结合情况，证实了这些基因上游不存在LexA结合位点。因此，结核分枝杆菌中很可能存在一种响应DNA损伤的基因调控替代机制。
