Overexpression of L-glutamine : D-fructose-6-phosphate amidotransferase provides resistance to methylmercury in Saccharomyces cerevisiae

To identify novel genes that confer resistance to methylmercury (MeHg), a y east genomic DNA library was transfected into Saccharomyces cerevisiae. Two functional plasmids were isolated from transfected yeast clones D1 and H5 that exhibited resistance to MeHg. The yeast transfected with plasmid isola ted from clone H5 was several-fold more resistant than yeast transfected wi th plasmid from clone D1. Functional characterization of the genomic DNA fr agment obtained from clone H5 determined that the GFA1 gene conferred resis tance to MeHg. GFA1 was reported to encode L-glutamine:D-fructose-6-phospha te amidotransferase (GFAT) which catalyzes the synthesis of glucosamine-6-p hosphate from glutamine and fructose-6-phosphate. Accumulation of mercury i n yeast clone W303B/pGFA1, which contains the transfected GFA1 gene, did no t differ from that in control yeast clone W303B/pYES2. The W303B/pGFA1 stra in did not show resistance to mercuric chloride, zinc chloride, cadmium chl oride or copper chloride, suggesting that the resistance acquired by GFA1 g ene transfection might be specific to MeHg. This is the first report of a g ene involved in MeHg resistance in eukaryotic cells identified by screening a DNA library. (C) 1999 Federation of European Biochemical Societies.