Characterization of a two component system, devR-devS, of Mycobacterium tuberculosis

By subtractive hybridization, we isolated genes, differentially expressed i n virulent strain (dev), that are expressed at higher levels in the virulen t Mycobacterium tuberculosis H37Rv strain in comparison to its avirulent co unterpart, H37Ra, and consequently may be associated with the virulence phe notype of M. tuberculosis. A two-component system, devR-devS, was identifie d by DNA sequencing of a dev clone. DevR, the predicted gene product of dev R, is a response regulator (RR) in the NarL/UhpA subfamily of two-component systems. The devS gene product displayed homology with histidine protein k inases (HPKs) including UhpB, NarX and NarQ. The devR-devS locus is precede d by gene Rv3134c that encodes a putative alanine-valine-rich protein. This locus was conserved in M. tuberculosis and M. bovis BCG but not in other m ycobacteria. A devR-lacZ transcription fusion demonstrated beta -galactosid ase activity in M. smegmatis and in M. tuberculosis. The devR and devS gene s were cotranscribed and the levels of their transcripts were lower in two isolates of the avirulent H37Ra strain in comparison to the virulent H37Rv strain of M. tuberculosis. The level of DevR protein was also lower in one of the H37Ra strains in comparison to the H37Rv strain. However, in a third isolate of H37Ra, RNA and protein expression was equivalent to that in the H37Rv strain. Electron microscopic immunogold analysis of M tuberculosis g rown in laboratory medium and within human monocytes revealed specific labe lling for DevR protein within the bacteria and the phagosomal lumen of infe cted monocytes. These findings collectively suggest a potential role for de vR-devS in the regulation of genetic programmes unique to the tubercle baci llus. (C) 2000 Harcourt Publishers Ltd.