FIG 4.
The arabinose and xylose systems are subject to transcriptional cross talk. (A) Xylose represses expression of the arabinose metabolic genes. (B) Arabinose represses expression of the xylose metabolic genes. The responses were 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 cells were grown in M9 minimal medium containing 0.4% glycerol and the specified concentrations of arabinose and xylose. Note that repression by arabinose was stronger than repression by xylose. Fluorescence values were averaged from single-cell, flow cytometry data. Error bars denote the standard deviations from three experiments performed on separate days. Histograms for these data are provided in Fig. S2 in the supplemental material.