Regulation of kas operon in mycobacteria:
The kas operon in mycobacteria comprises a set of five genes which enables the characteristic elongation of FAS-I generated fatty acyl primers to long carbon chain fatty acids, mycolic acids. These genes transcriptionally respond to antimycobacterial drugs, upon exposure to intracellular and extracellular stresses and during macrophage infection. This implies that their cis-regulatory regions employ, possibly, a network of transcriptional regulators to modulate the expression of kas operon genes during different cellular states. We deciphered the orthologous kas operon promoters from different mycobacterial species and identified thirteen sequence motifs corresponding to different families of transcriptional regulators. Using a panel of recombinant strains carrying promoter deletions, the influence of these motifs on the reporter gene expression was examined.

A FadR homologue in M. tuberculosis, Rv0494, was identified, which binds to its operator in the upstream region of the kas operon. We have shown that FadRMt (Rv0494) directly binds to long-chain fatty acyl-CoA and the FadR-DNA binding can be impaired by long-chain fatty acyl-CoA compounds. Overexpression of Rv0494 in Mycobacterium bovis BCG reduced the basal level expression of kas operon genes, thereby suggesting the repressor nature of this protein in FAS-II regulation. This is the first report of a GntR/FadR family protein acting as a fatty acid-responsive transcriptional regulator in M. tuberculosis, suggesting a possible role for this protein in mycolic acid biosynthesis. Our findings suggest that in mycobacteria the expression of kas operon genes is orchestrated by a network of transcriptional regulators. The structural conservation of transcription factors binding motifs suggests a high degree of functional relatedness in expression of kas operon genes in mycobacteria. (Microbiology, 2013)

Functional genomics of sigma factors in mycobacteria :
In M. smegmatis, sigF is widely expressed during different growth stages and plays role in adaptation to stationary phase and oxidative stress. Using a sigF deletion mutant of M. smegmatis mc2155, we demonstrate that SigF is not essential for growth of bacterium. Deletion of sigF results in loss of carotenoid pigmentation which rendered increased susceptibility to H2O2 induced oxidative stress in M. smegmatis. SigF modulates the cell surface architecture and lipid biosynthesis extending the repertoire of SigF function in this species. M. smegmatis SigF regulon included variety of genes expressed during exponential and stationary phases of growth and those responsible for oxidative stress, lipid biosynthesis, energy and central intermediary metabolism.

                                             M. smegmatis wild type                                                        M. smegmatis sigF deletion mutant

2D-DIGE profile of wild type and ΔsigF mutant proteins