Transcriptional regulation of glutathione synthetase in the fission yeast Schizosaccharomyces pombe

Glutathione (GSH), an important antioxidant involved in the stress response, is synthesized in two sequential reactions involving glutamylcysteine synthetase (GCS), followed by glutathione synthetase (GS). Expression of the unique GS gene in the fission yeast Schizosaccharomyces pombe was previously found to be regulated by nitric oxide and by L-buthionine-(S,R)-sulfoximine (BSO), a specific inhibitor of GCS. In this work, expression of S. pombe GS gene is shown to be induced by menadione (MD), which generates superoxide. The responsible DNA sequence between -365 and -234 bp from the translation start site, was convinced using five GS-lacZ fusion plasmids. Expression of GS gene is also induced by low glucose, fructose and disaccharides, apparently dependent on Pap1 protein; GS mRNA increases in low concentrations of glucose in wild type S. pombe but not in Pap1-negative cells. Although nonfermentable carbon sources such as acetate and ethanol stimulate expression of GS gene, they also arrest the growth of the yeast cells. These results indicate that the biosynthesis of glutathione is regulated by superoxide radicals and carbon source limitation.