In response to stresses, Mycobacterium cells become dormant. This process is regulated by the DosR transcription factor. In Mycobacterium tuberculosis, the dormancy regulon is well characterized and contains the dosR gene itself and dosS and dosT genes encoding DosR kinases, nitroreductases (acg; Rv3131), diacylglycerol acyltransferase (DGAT) (Rv3130c), and many universal stress proteins (USPs). In this study, we apply comparative genomic analysis to characterize the DosR regulons in nine Mycobacterium genomes, Rhodococcus sp. RHA1, Nocardia farcinica, and Saccharopolyspora erythraea. The regulons are highly labile, containing eight core gene groups (regulators, kinases, USPs, DGATs, nitroreductases, ferredoxins, heat shock proteins, and the orthologs of the predicted kinase [Rv2004c] from M. tuberculosis) and 10 additional genes with more restricted taxonomic distribution that are mostly involved in anaerobic respiration. The largest regulon is observed in M. marinum and the smallest in M. abscessus. Analysis of large gene families encoding USPs, nitroreductases, and DGATs demonstrates a mosaic distribution of regulated and nonregulated members, suggesting frequent acquisition and loss of DosR-binding sites.