Fig 3.

The vanillate-inducible gene expression system for M. xanthus. (A) Schematic showing how expression of a candidate gene (“gene X”), placed under the control of the vanillate promoter, P_van, and located in the vanR-vanAB intergenic region, is turned off by the VanR repressor binding to its operator at P_van in the absence of vanillate. VanR is transcribed constitutively and in the direction opposite to that of P_van. Vanillate, when present, binds to VanR, preventing binding of its operator and allowing transcription of gene X from P_van. (B) Expression of P_van::lacZ with and without 0.5 mM vanillate after 15 to 20 h, shown in terms of the β-galactosidase-specific activity measured in three independent experiments. Plasmids V₁ (pMR3564, Km^r; pMR3632, Tc^r) contain only the vanR-vanAB intergenic region for vanR expression, while plasmids V₂ (pMR3639, Km^r; pMR3638, Tc^r) express vanR constitutively from P_R3–4 (see the text). (C) P_van::lacZ expression in the presence of vanillate at higher (left panel) or lower (right panel) concentrations for strain MR2469 (with P_R3–4::vanR). (D) Time dependence of P_van::lacZ expression in the presence of 0.5 mM vanillate for strain MR2453 (with P_vanR::vanR). In panels B, C, and D, β-galactosidase-specific activities correspond to the means and standard deviations of the means (error bars) of the results of three independent measurements of samples collected from cultures with an OD₅₅₀ of 0.9 to 1.1.