Increased levels ofsigJmRNA in late stationary phase cultures ofMycobacterium tuberculosisdetected by DNA array hybridisation

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Abstract
In order to determine which genes are involved in maintaining viability of 100-day stationary-phase bacteria and persistent bacteria after antibiotic treatment, we used a mini-DNA array to examine the transcription of 82 genes of M. tuberculosis in the 100-day stationary-phase cultures before and after rifampicin treatment. We found that the mRNA level of a sigma factor gene, sigJ, was strongly up-regulated in the late stationary-phase cultures. Other genes were also up-regulated, although to a lesser extent than sigJ. Surprisingly, after rifampicin treatment there was no significant change in sigJ expression, and most of the other 82 genes in the mini-DNA array also maintained expression, some at relatively high levels. These results suggest that SigJ may control gene expression in the quiescent state and may be an important component in the mechanisms by which M. tuberculosis survives prolonged stationary phase even in the presence of sterilising antibiotics.