GLUCOSE-UPTAKE AND METABOLISM IN GRR1 CAT80 MUTANTS OF SACHAROMYCES-CEREVISIAE/

Glucose repression in the yeast Saccharomyces cerevisiae designates a global regulatory system controlling the expression of various sets of genes required for the utilization of alternate carbon sources. In a screen, designed for the selection of mutants with reduced glycolytic flux we obtained isolates which were shown by complementation of the c loned wild-type gene to be allelic to the glucose repression mutants g rr1/cat80/cot2 previously described. We demonstrate that the grr1 lesi on lead to a concentration-dependent decrease in glycolytic flux on gl ucose. It is very likely that this is caused by a significant decrease in the expression of various genes encoding hexose transporters (HXT1 ,3) leading to a reduced glucose-uptake rate. In contrast, expression of the maltose permease gene (MAL11) and maltose utilization is normal . There is indirect evidence that grr1 affects the uptake of amino aci ds, and others have shown that the sugar-induced transport of divalent cations is impaired. These effects are not glucose-specific. We sugge st that Grr1, a putative cytoplasmic protein, has a central function i n the sensing of nutritional conditions for a variety of unrelated sub stances, and that relief from glucose repression may be a corollary of this defect in sensing.