An accurate method for the qualitative detection and quantification of mycobacterial promoter activity.

The present study was designed to determine the half-life of gfp(m) (2+) mRNA, which encodes mycobacterial codon-optimised highly fluorescent GFP(m) (2+) protein, and to find out whether mycobacterial promoter activity can be quantitated more accurately using the mRNA levels of the reporter gene, gfp(m) (2+), than the fluorescence intensity of the GFP(m) (2+) protein. Quantitative PCR of gfp(m) (2+) mRNA in the pulse-chased samples of the rifampicin-treated Mycobacterium smeg-matis/gfpm(2+) transformant showed the half-life of gfp(m) (2+) mRNA to be 4.081 min. The levels of the gfp(m) (2+) mRNA and the fluorescence intensity of the GFP(m) (2+) protein, which were expressed by the promoters of Mycobacterium tuberculosis cell division gene, ftsZ (MtftsZ), were determined using quantitative PCR and fluorescence spectrophotometry, respectively. The data revealed that quantification of mycobacterial promoter activity by determining the gfp(m) (2+) mRNA levels is more accurate and statistically significant than the measurement of GFP(m) (2+) fluorescence intensity, especially for weak promoters.

Cloning, expression, purification, and biochemical characterisation of the FIC motif containing protein of Mycobacterium tuberculosis.

The role of FIC (Filamentation induced by cAMP)(2) domain containing proteins in the regulation of many vital pathways, mostly through the transfer of NMPs from NTPs to specific target proteins (NMPylation), in microorganisms, higher eukaryotes, and plants is emerging. The identity and function of FIC domain containing protein of the human pathogen, Mycobacterium tuberculosis, remains unknown. In this regard, M. tuberculosis fic gene (Mtfic) was cloned, overexpressed, and purified to homogeneity for its biochemical characterisation. It has the characteristic FIC motif, HPFREGNGRSTR (HPFxxGNGRxxR), spanning 144th to 155th residue. Neither the His-tagged nor the GST-tagged MtFic protein, overexpressed in Escherichia coli, nor expression of Mtfic in Mycobacterium smegmatis, yielded the protein in the soluble fraction. However, the maltose binding protein (MBP) tagged MtFic (MBP-MtFic) could be obtained partly in the soluble fraction. The cloned, overexpressed, and purified recombinant MBP-MtFic showed conversion of ATP, GTP, CTP, and UTP into AMP, GMP, CMP, and UMP, respectively. Sequence alignment with several FIC motif containing proteins, complemented with homology modeling on the FIC motif containing protein, VbhT of Bartonella schoenbuchensis as the template, showed conservation and interaction of residues constituting the FIC domain. Site-specific mutagenesis of the His144, or Glu148, or Asn150 of the FIC motif, or of Arg87 residue that constitutes the FIC domain, or complete deletion of the FIC motif, abolished the NTP to NMP conversion activity. The design of NMP formation assay using the recombinant, soluble MtFic would enable identification of its target substrate for NMPylation.