Patent ID: 7410790

Claim:
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.