Biosynthesis of phytochelatins in the fission yeast. Phytochelatin synthesis: A second role for the glutathione synthetase gene of Schizosaccharomyces pombe

By complementation screening of a cadmium-sensitive Schizosaccharomyces pom be mutant deficient in phytochelatin synthesis, but with 44% of the wild-ty pe glutathione content, we cloned a DNA fragment involved in phytochelatin synthesis. Sequence analysis revealed that it encodes the second enzyme inv olved in glutathione (GSH) biosynthesis, glutathione synthetase (GSH2) (E.C .6.3.2.3, Wang and Oliver, 1997). The mutant allele shows a single base-pai r exchange at the 3' end of the reading frame leading to a single amino aci d change from glycine to aspartate. This mutation leads to a significant re duction of phytochelatin synthesis, whereas glutathione synthesis is impair ed to a far lesser extent. Complementation with the Arabidopsis thaliana GS H2 cDNA led to a partial restoration of phytochelatin synthesis. These data strongly suggest that the GSH2 gene encodes a bifunctional enzyme that is able to catalyse both the synthesis of GSH by adding glycine to the dipepti de (gamma Glu-Cys) and the synthesis of phytochelatins. The sequence has be en submitted to EMBL, Accession No. Y08414. Copyright (C) 1999 John Wiley & Sons, Ltd.