The Mycobacterium tuberculosis katG promoter region contains a novel upstream activator.

An Escherichia coli-mycobacterial shuttle vector, pJCluc, containing a luciferase reporter gene, was constructed and used to analyse the Mycobacterium tuberculosis katG promoter. A 1.9 kb region immediately upstream of katG promoted expression of the luciferase gene in E. coli and Mycobacterium smegmatis. A smaller promoter fragment (559 bp) promoted expression with equal efficiency, and was used in all further studies. Two transcription start sites were mapped by primer extension analysis to 47 and 56 bp upstream of the GTG initiation codon. Putative promoters associated with these show similarity to previously identified mycobacterial promoters. Deletions in the promoter fragment, introduced with BAL-31 nuclease and restriction endonucleases, revealed that a region between 559 and 448 bp upstream of the translation initiation codon, designated the upstream activator region (UAR), is essential for promoter activity in E. coli, and is required for optimal activity in M. smegmatis. The katG UAR was also able to increase expression from the Mycobacterium paratuberculosis P(AN) promoter 15-fold in E. coli and 12-fold in M. smegmatis. An alternative promoter is active in deletion constructs in which either the UAR or the katG promoters identified here are absent. Expression from the katG promoter peaks during late exponential phase, and declines during stationary phase. The promoter is induced by ascorbic acid, and is repressed by oxygen limitation and growth at elevated temperatures. The promoter constructs exhibited similar activities in Mycobacterium bovis BCG as they did in M. smegmatis.

Involvement of the N- and C-terminal domains of Mycobacterium tuberculosis KatG in the protection of mutant Escherichia coli against DNA-damaging agents.

The Mycobacterium tuberculosis KatG enzyme, like most hydroperoxidase I (HPI)-type catalases, consists of two related domains, each with strong similarity to the yeast cytochrome c peroxidase. The catalase-peroxidase activity is associated with the amino-terminal domain but currently no definite function has been assigned to the carboxy-terminal domain, although it may play a role in substrate binding. This paper reports another possible function of the KatG protein involving protection of the host cell against DNA-damaging agents. The M. tuberculosis katG gene, the 5' domain and the 3' domain were cloned separately, in-frame with the maltose-binding protein, into the vector pMAL-c2. These constructs were introduced into four DNA-repair mutants of Escherichia coli, DK1 (recA), AB1884 (uvrC), AB1885 (uvrB) and AB1886 (uvrA), which were then tested for their ability to survive treatment with UV light (254 nm), hydrogen peroxide (1.6 mg ml-1) and mitomycin C (6 micrograms ml-1). All three constructs conferred resistance to UV upon the recA E. coli cells, whereas resistance to mitomycin C was found in all repair mutants tested. Protection against hydrogen peroxide damage was less pronounced and predominantly found in the recA host. These results indicated that the M. tuberculosis katG gene can enhance DNA repair in E. coli, and that the 5' and 3' domains can function separately. UV sensitivity tests on Mycobacterium intracellulare and M. tuberculosis strains mutant in katG revealed that the katG gene product does not play an additive role in the survival of mycobacterial cells after exposure to short-wavelength UV irradiation, in repair-competent cells.