SummaryThe search for new TB drugs that rapidly and effectively sterilize the tissues and are thus able to shorten the duration of chemotherapy from the current 6 months has been hampered by a lack of understanding of the metabolism of the bacterium when in a 'persistent' or latent form. Little is known about the condition in which the bacilli survive, although laboratory models have shown that Mycobacterium tuberculosis can exist in a non-growing, drug-resistant state that may mimic persistence in vivo. Using nutrient starvation, we have established a model in which M. tuberculosis arrests growth, decreases its respiration rate and is resistant to isoniazid, rifampicin and metronidazole. We have used microarray and proteome analysis to investigate the response of M. tuberculosis to nutrient starvation. Proteome analysis of 6-week-starved cultures revealed the induction of several proteins. Microarray analysis enabled us to monitor gene expression during adaptation to nutrient starvation and confirmed the changes seen at the protein level. This has provided evidence for slowdown of the transcription apparatus, energy metabolism, lipid biosynthesis and cell division in addition to induction of the stringent response and several other genes that may play a role in maintaining longterm survival within the host. Thus, we have generated a model with which we can search for agents active against persistent M. tuberculosis and revealed a number of potential targets expressed under these conditions.

Paired helical filaments (PHFs) are the structural constituents of neurofibrillary tangles in Alzheimer's disease and are composed of hyperphosphorylated forms of the microtubule‐associated protein tau (PHF‐tau). Pathological hyperphosphorylation of tau is believed to be an important contributor to the destabilisation of microtubules and their subsequent disappearance from tangle‐bearing neurons in Alzheimer's disease, making elucidation of the mechanisms that regulate tau phosphorylation an important research goal. Thus, it is essential to identify, preferably by direct sequencing, all of the sites in PHF‐tau that are phosphorylated, a task that is incomplete because of the difficulty to date of purifying insoluble PHF‐tau to homogeneity and in sufficient quantities for structural analysis. Here we describe the solubilisation of PHF‐tau followed by its purification by Mono Q chromatography and reversed‐phase HPLC. Phosphopeptides from proteolytically digested PHF‐tau were sequenced by nanoelectrospray mass spectrometry. We identified 22 phosphorylation sites in PHF‐tau, including five sites not previously identified. The combination of our new data with previous reports shows that PHF‐tau can be phosphorylated on at least 25 different sites.

The anti-tuberculosis drug ethionamide (ETH), which is a structural analog of isoniazid (INH), is known to strongly inhibit mycolic acid synthesis in Mycobacterium tuberculosis. While several targets have been identified for INH, only speculative information is available concerning ETH. Mutations within the promoter and the coding region of enoyl-ACP reductase (InhA) were found to confer resistance to both drugs, thus leading to the impression that INH and ETH may share a common mode of action. However, a notable distinction between the two drugs lies in the lack of cross-resistance in clinical isolates. This may be attributed in part to the fact that the pro-drug INH must be activated via KatG, and no activation step for ETH has yet been described. Here we report the identification of an activator for ETH. The ETH activator (Rv3854c), which we have termed EthA, was found to be homologous to various monooxygenases and induced ETH sensitivity when over-expressed in mycobacteria. Interestingly, the neighbouring open reading frame (Rv3855), which was found homologous to transcriptional repressors of the tetR family, led to ETH resistance when over-expressed. In addition, chromosomal inactivation of this gene by transposition led to ETH hyper-sensitivity. These data strongly suggest that Rv3855, which we have termed EthR, regulates the production of EthA which subsequently activates the pro-drug ETH. This study opens up new avenues of research relating to ETH activation in mycobacteria, -possibly leading to an improved efficacy of ETH and to the generation of new anti-mycobacterial agents.

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Two-component regulatory systems have been widely implicated in bacterial virulence. To investigate the role of one such system in Mycobacterium tuberculosis, a strain was constructed in which the senX3-regX3 system was deleted by homologous recombination. The mutant strain (Tame15) showed a growth defect after infection of macrophages and was attenuated in both immunodeficient and immunocompetent mice. Competitive hybridization of total RNA from the wild-type and mutant strains to a whole-genome microarray was used to identify changes in gene expression resulting from the deletion. One operon was highly up-regulated in the mutant, indicating that regX3 probably has a role as a repressor of this operon. Other genes which were up-or down-regulated were also identified. Many of the genes showing down-regulation are involved in normal growth of the bacterium, indicating that the mutant strain is subject to some type of growth slow-down or stress. Genes showing differential expression were further grouped according to their pattern of gene expression under other stress conditions. From this analysis 50 genes were identified which are the most likely to be controlled by RegX3. Most of these genes are of unknown function and no obvious motifs were found upstream of the genes identified. Thus, it has been demonstrated that the senX3-regX3 two-component system is involved in the virulence of M. tuberculosis and a number of genes controlled by this system have been identified.