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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.