Analysis of the dormancy-inducible narK2 promoter in Mycobacterium bovis BCG.

Upon depletion of oxygen, the obligate aerobe mycobacteria switch from growth to a state of non-replicating persistence or dormancy. Here, we report the first functional analysis of a dormancy-dependent mycobacterial promoter in Mycobacterium bovis BCG. Promoter probing using a 'lacZ reporter detected a dormancy-inducible promoter activity upstream of the coding sequence for the putative nitrite extrusion protein NarK2. Primer extension analysis mapped a transcriptional start point 47 bp upstream of the narK2 start codon. Deletion analysis revealed that the sequence -222 to -133 bp upstream from the transcriptional start point was required for basal and dormancy-inducible reporter expression. The sequence +1 to +47 downstream of the transcriptional start point had a strong inhibitory effect on the level of dormancy-induced beta-galactosidase activity. The identification of apparent activating and inhibiting regions suggests that the narK2 promoter is at least under dual control.