Differential regulation of three genes encoding glutathione S-transferases in Schizosaccharomyces pombe

Glutathione S-transferases (GSTs) are detoxifying enzymes that catalyze the conjugation of glutathione with a variety of reactive electrophilic compounds. Three GST genes were previously characterized in the fission yeast Schizosaccharomyces pombe. In this work, we examined the transcriptional regulation of these genes using individual GST-lacZ fusions and RT-PCR. Basal synthesis of β-galactosidase from the GSTII-lacZ fusion was higher than from the GSTI-lacZ and GSTIII-lacZ fusion. Diethylmaleate (0.2 mM) greatly enhanced the synthesis of β-galactosidase from the GSTII-lacZ fusion, but did not affect synthesis from the other two fusion genes. A switch to 0.3% glucose or 0.3% sucrose as sole carbon source enhanced expression from the GSTIII-lacZ fusion gene, while sodium nitroprusside (1.5 mM), tert-butylhydroquinone (0.2 mM), and L-buthionine-[S,R]-sulfoximine (0.01 mM) increased expression of the GSTII gene. The effects of these agents on GST mRNA levels were confirmed by measurements employing RT-PCR. Our results suggest that transcription of the three S. pombe GST genes is subjected to differential regulation under various stress conditions, and may be linked to their different physiological functions.