New insights into the activation of o-xylene biodegradation in Pseudomonasstutzeri OX1 by pathway substrates

The regulation of the tou operon of Pseudomonas stutzeri OX1, for degradati on of toluene and o-xylene via phenolic intermediates, has been faithfully reconstructed in vitro with purified proteins. The set-up included the prok aryotic enhancer-binding protein TouR, the sigma (54)-dependent P-ToMO prom oter and the sigma (54)-containing RNA polymerase. With this system we prov e that direct binding of 2-methylphenol (o-cresol) to TouR is the only regu latory step for activation of P-ToMO in response to aromatic effecters, the reby ruling out the involvement of other factors or a need for protein proc essing. In addition, we found that while TouR failed entirely to activate P -ToMO in the absence of inducers, the protein had per se a very significant ATPase activity, which was only moderately increased by o-cresol addition. The results presented here support the view that TouR-like proteins are pa rticularly suitable as evolutionary assets to endow recently evolved pathwa ys for the degradation of environmental pollutants with an optimal degree o f transcriptional regulation.