24 Analysis of Mycobacterial Differential Gene Expression by RAP-PCR

Mycobacteria, like other bacteria, respond to environmental signals with changes in gene expression regulated at the level of transcription. The significance of gene-expression patterns in pathogens, such asMycobacterium tuberculosis, is that specific signals encountered durmg the process of mfection regulate, often via two component regulatory systems, the expression of vn-ulence genes necessary for that stage of host-pathogen mteraction. Signals known to Induce bacterial gene expression include temperature, osmolarity, oxidative stress, pH, low oxygen tension, nutrient deprivation, and Fe²⁺ limitation different conditions inducing different, but overlapping subsets of genes (1 ), sometimes referred to as stimulons, regulons, or virulons. Little is known about gene-expression patterns of mycobacteria and the definition of differentially -expressed genes is central to understanding pathogenesis and virulence at a molecular level.