Identification and cloning of genes differentially expressed in the virulent strain of Mycobacterium tuberculosis.

The mechanism(s) used by Mycobacterium tuberculosis to establish disease in the human host are not well understood. The virulent M. tuberculosis H37Rv strain and its avirulent derivative M. tuberculosis H37Ra provide an attractive system for the identification of virulence-specific genes of the tubercle bacillus. Differentially expressed genes in the virulent strain of M. tuberculosis (dev genes) were identified by screening a plasmid gene bank of H37Rv with a cDNA probe that was enriched in dev transcripts by subtraction of RNAs common to H37Ra. Individual dev clones coded for RNA transcripts that were differentially expressed in H37Rv in comparison to H37Ra. In contrast, mRNAs and stable RNAs that were commonly expressed in both the strains were present in equivalent amounts. The identification and cloning of dev genes marks the first step in defining bacterial gene(s) involved in the pathogenesis of M. tuberculosis.