Glutathione S-transferases (GSTs) are a family of multifunctional enzymes that play critical roles in the detoxification of xenobiotics and the protection of tissues against oxidative damage. GSTs are important enzymes in plant responses to a number of environmental stresses including herbicides and pathogen attack. Ocs elements are a group of related, 20 bp promoter elements which have been exploited by some plant pathogens to express genes in plants. Ocs elements have also been found to regulate the expression of a plant GST promoter. An Arabidopsis GST gene, called GST6 has been isolated. GST6 expression is under tissue-specific control and is induced following treatment with auxin, salicylic acid and H2O2. The GST6 promoter contains a binding site for two Arabidopsis ocs element binding factors (OBF), that has some sequence homology to ocs element sequences. Interestingly, OBP1 (OBF binding protein), a DNA-binding protein that was isolated by screening an Arabidopsis cDNA library with a labeled OBF protein as a probe, binds next to the OBF-binding site on the GST6 promoter. OBP1 was able to significantly stimulate the binding of OBF proteins to the GST6 promoter, raising the possibility that interactions between the OBP1 and OBF proteins may be important for GST6 expression.