FIG 5.
Xylose does not repress arabinose gene expression in the absence of XylR (ΔxylR mutant strain) (A) but does in the absence of xylose metabolism (ΔxylAB mutant strain) (B). The responses were measured in the specified strain containing a single-copy, chromosomal transcriptional fusion of the ParaB promoter to the Venus fluorescent protein. The cells were grown in M9 minimal medium containing 0.4% glycerol and the specified concentrations of arabinose and 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. S3 in the supplemental material.