Fig. 2.
Promoter activity of the Mtb senX3 promoter and the Mtb senX3-regX3 IR, as measured by β-galactosidase assay. Fluorescence units represent β-galactosidase activity produced by LacZ, whose expression is driven by the promoters of interest, after 24 h exposure to Middlebrook 7H9 broth (black bars), Pi depletion (0 µM Pi; white bars) and nutrient starvation (NS; grey bars). C2FDG was used as fluorescent substrate. pYUB76-containing Mtb CDC1551 showed similar background activity, regardless of condition. (a) pSR showed stronger promoter activity following Mtb exposure to NS (P<0.01) and 0 µM Pi (P<0.05) relative to exponential growth in 7H9 broth. (b) Promoter activity of the IR increased with increasing number of MIRUs during NS (P<0.01). pIR-2 showed stronger promoter activity during Mtb exposure to NS (P<0.01) and 0 µM Pi (P<0.01) than during growth in 7H9 broth. Error bars represent sd of the mean. *P<0.05; **P<0.01.