The high sequence conservation of the KstR transcription factor is mirrored in the conservation of KstR binding sites across numerous promoters. KstR binding sites are known to be highly conserved across the Mycobacteria, out to Rhodococcus and Nocardia [36] . These sites are conserved in both sequence and position within their respective promoters. In our analysis, both in searches using known transcription factor binding motifs, as well as in our de novo motif searches, a subset of KstR binding sites are the most conserved transcription factor motifs observed. They are also among the most conserved of any noncoding sequence we identified. The conservation of the KstR gene and binding sites, the emergence of KstR at the ancestor of Rhodococcus and the Mycobacteria, and the loss of KstR paralogs within the pathogenic Mycobacteria, suggests that this transcription factor and its evolving regulon have played an important role in the expansion of lipid metabolism and its adaptation to pathogenicity in Mtb.