Role of the sulphate assimilation pathway in utilization of glutathione asa sulphur source by Saccharomyces cerevisiae

Mutants unable to grow on medium containing glutathione as a sole source of sulphur (GSH medium) were isolated from Saccharomyces cerevisiae strains c arrying met17 (deficiency of O-acetylserine and O-acetylhomoserine sulphydr ylase). They were defective in the high-affinity glutathione transport syst em, GSH-P1. Newly acquired mutations belonged to the same complementation g roup, gsh11. However, it became apparent that gsh11 conferred the mutant ph enotype not by itself but in collaboration with met17. Moreover, mutations conferring the defect in sulphate assimilation made the cell unable to grow on GSH medium in collaboration with gsh11. From this finding, we propose t hat the sulphate assimilation pathway acts as a sulphur-recycling system an d that this function is especially vital to the cell when the supply of glu tathione is limited. Copyright (C) 1999 John Wiley & Sons, Ltd.