Method for producing γ-glutamylcysteine

An isolated yeast which has a γ-glutamylcysteine-producing ability and is auxotrophic for pantothenic acid, wherein γ-glutamylcysteine content per dried cells of the yeast increases in course of time when the yeast is cultured in a medium containing a limited amount of pantothenic acid,

• wherein said yeast comprises a mutated endogenous chromosomal polynucleotide sequence encoding glutathione synthetase wherein said mutation reduces or eliminates gluthathione synthetase activity, and
• wherein said yeast further comprises a mutated MET30 gene wherein the mutation replaces serine at position 569 of a protein encoded by the MET30 gene with phenylalanine and wherein expression of said mutated MET30 gene derepresses expression of the endogenous MET25 gene,
• wherein said polynucleotide encoding said glutathione synthetase hybridizes with the polynucleotide of SEQ ID NO:
• 1 under stringent conditions,
• wherein said MET30 gene hybridizes with the polynucleotide of SEQ ID NO:
• 3 under stringent conditions, and
• wherein said stringent conditions comprise washing at 60° in 0.1×SSC and 0.1% SDS.