The characterization of conserved binding motifs and potential target genes for M. tuberculosis MtrAB reveals a link between the two-component system and the drug resistance of M. smegmatis

Background: The two-component systems of Mycobacterium tuberculosis are apparently required for its growth and resistance in hostile host environments. In such environments, MtrAB has been reported to regulate the expression of the M. tuberculosis replication initiator gene, dnaA. However, the dnaA promoter binding sites and many potential target genes for MtrA have yet to be precisely characterized. Results: In this study, a 7 bp sequence motif in the dnaA promoter region was identified for MtrA binding using DNasel footprinting assays and surface plasmon resonance (SPR) analysis. Approximately 420 target genes potentially regulated by MtrA, including the isoniazid inducible gene iniB, were further characterized from M. tuberculosis and M. smegmatis genomes. When assayed using quantitative real-time PCR (qRT-PCR), many of the target genes demonstrated significant expression changes when the antisense mRNA of the mtrA gene was expressed in M. smegmatis. The recombinant mycobacteria grew in length and were more sensitive to two anti-tuberculosis drugs, isoniazid and streptomycin. Conclusions: These findings yield critical information about the regulatory mechanisms of the MtrAB two-component system and its role in the drug resistance of M. smegmatis.