A chromate-tolerant mutant chr1-663T bearing a stable one-gene mutation and its parental strain 6chr+ were used to investigate the background of CrVI tolerance in the fission yeast Schizosaccharomyces pombe. The mutant chr1-663T displayed a significantly decreased specific glutathione reductase (GR) activity coded by the pgr1 + gene compared with its parental strain. Transformants of the mutant chr1-663T with a nonintegrative pUR18N vector expressing the pgr1 + gene exhibited the same Cr VI sensitivity and specific GR activity as their parental strain, demonstrating the importance of the GR-NADPH system in CrVI tolerance. Transformants, nevertheless, exhibited an increased intracellular peroxide concentration, a decreased CrVI-reducing and HO•-producing ability, which suggested an unbalanced oxidoreduction state of cells and partial complementation of the GR function. No mutation was found in the sequences of the pgr1 + and the pap1 + (transcriptional regulatory gene of GR) genes of the CrVI-tolerant mutant by sequence analysis.
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