• Phosphoglucose isomerase;
  • Glucose toxicity;
  • Saccharomyces;
  • Glycolysis

Abstract Glucose inhibits growth of yeast phosphoglucose isomerase mutants in permissive media. Mutants insensitive to this effect were isolated by selection on media containing 2% fructose + 2% glucose. A nuclear, monogenic, recessive mutation named rgl was responsible for this phenotype. The mutants isolated belonged to two complementation groups and have been termed rgl1 and rgl2. When the double mutants were grown on fructose, fermentation of fructose or glucose was similar to that of the parental pgi strain but was not measurable when grown on fructose + glucose. Under these conditions, respiration of glucose and to a lesser extent of fructose was enhanced. The double mutants pgi rgl did not grow on fructose + glucose in the presence of antimycin A or ethidium bromide and their cytochrome oxidase was no longer sensitive to glucose repression. The results are interpreted as an indication that in the double mutants the glucose may be channeled through the pentose phosphate pathway to respiration.