The glutathione-mediated detoxification pathway in yeast: an analysis using the red pigment that accumulates in certain adenine biosynthetic mutants of yeasts reveals the involvement of novel genes

Abstract

The glutathione-mediated pathway for the detoxification of endogenously and exogenously derived toxic compounds was investigated using a pigment that accumulates in certain adenine biosynthetic mutants of yeasts. The ade1 / ade2 mutants of Saccharomyces cerevisiae, when grown on adenine-limiting medium, accumulate a characteristic red pigment (ade pigment) in their vacuoles. The precursors of the ade pigments are toxic intermediates that form conjugates with glutathione, followed by their transport inside the vacuole. In this study, this red pigment was used as a phenotypic screen to obtain insight regarding new genes involved in the three phases of this detoxification pathway: the activation phase (phase I), the conjugation phase (phase II), and the efflux phase (phase III). Components of the phase III (efflux) pathway which includes, in addition to the previously characterized Ycf1p and Bpt1p, another member of the 'Ycf1p family', Bat1p, as well as a vacuolar H+-ATPase-dependent transport were identified. In the investigation of phase II (conjugation), it was found that glutathione S-transferases, encoded by GTT1 and GTT2,do not appear to play a role in this process. By contrast, two other previously characterized genes, the oxidative stress transcription factor gene, SKN7 , and the yeast caesin protein kinase gene, YCK1, of S. cerevisiae do participate in this pathway.