IDENTIFICATION OF EXTRAGENIC SUPPRESSORS OF THE CIF1 MUTATION IN SACCHAROMYCES-CEREVISIAE

The cif1 mutation of Saccharomyces cerevisiae causes inability to grow on glucose and related fermentable carbon sources. We have isolated t wo different suppressor mutations that allow growth on glucose of yeas ts carrying the cif1 mutation. One of them, sci1-1, is recessive and c aused inability to grow on non-fermentable carbon sources and to de-re press fructose-1,6-bisphosphatase. The other suppressor mutation, SCI2 -1, is dominant and diminished the capacity to phosphorylate glucose o r fructose. The SCT2-1 mutation decreased sporulation efficiency by 70 % in heterozygosis and by more than 90% in homozygosis. In a CIF1 back ground, cells carrying the mutation SCI2-1 accumulated trehalose durin g the logarithmic phase of growth and hyperaccumulated it during the s tationary phase. Genetic tests showed that SCI2 was either allelic, or else closely linked, to HXK2. The concentrations of the glycolytic me tabolites measured during growth on glucose in cells carrying the cif1 mutation and any of the suppressor mutations were similar to those of a wild-type. Both types of suppresser mutations restored the transien t cAMP response to glucose to cif1 mutants.