FIG. 4.

Increased ytxR expression induces a Φ(ytxA-lacZ) operon fusion. (A) Expression of Φ(ytxA-lacZ) in the presence (+) or absence (−) of IPTG in a strain without a transposon (YVM619) or two mutants with tacp transposon insertions upstream of ytxR (AJD199 and AJD200). (B) Expression of Φ(ytxA-lacZ) in ytxR⁺ (YVM619) or ΔytxR null (AJD254) strains with either araBp-ytxR⁺ expression plasmid pAJD593 (+) or the pBAD18-Km control vector (−). Cultures were grown and β-galactosidase activities were determined as described in Materials and Methods. The data are averages from three independent cultures, and the error bars indicate the standard deviations from the means. Sp. Act., specific activity.