Fig 6.

Fluorescence intensities and distributions of GFP and RFP variants expressed by different promoters on multicopy plasmids. A minimum of 300 cells per strain was counted and the fluorescence intensity per cell measured as described in Materials and Methods. In panel A, the average fluorescence intensity per FP variant is shown in arbitrary units in the FITC channel (GFP; black bars) and the TRITC channel (RFP; gray bars) for each studied promoter (from left to right, P_secA, P_upp, P_cotD, and P_sigG). Error bars are not included, due to a wide distribution of signal intensity for some promoters (the error bars would then exceed 50%). This variation of fluorescence for all cells is visualized in panel B. Signal intensities (in arbitrary units [AU]) were grouped (x axis), and the number of fluorescent cells per group was calculated (y axis). The distribution of fluorescence intensity is shown for GFPmut3a (light gray shading), sfGFP(Bs) (dark gray shading), GFP(Sp) (black shading), mCherry (white shading), and mKate2 (patterned shading).