FIG 2.
Both the arabinose and xylose systems exhibit a bimodal response to their cognate sugar. The response was measured in a single strain containing single-copy, chromosomal transcriptional fusions of the ParaB promoter to the Venus fluorescent protein and the PxylA promoter to the mCherry fluorescent protein. The density plots show the distributions of promoter activities in individual cells as determined based on Venus and mCherry fluorescence. Data were smoothed and normalized to a peak value of 100 to facilitate interpretation. The cells were grown in M9 minimal medium containing 0.4% glycerol and various concentrations of arabinose (A) or xylose (B) as indicated. Table S1 in the supplemental material lists the fractions of cells in the uninduced and induced states.