EVIDENCE FOR TREHALOSE-6-PHOSPHATE-DEPENDENT AND TREHALOSE-6-PHOSPHATE-INDEPENDENT MECHANISMS IN THE CONTROL OF SUGAR INFLUX INTO YEAST GLYCOLYSIS

In the yeast Saccharomyces cerevisiae, trehalose-6-phosphate (tre-6-P) synthase encoded by GGS1/TPS1, is not only involved in the production of trehalose but also in restriction of sugar influx into glycolysis in an unknown fashion; it is therefore essential for growth on glucose or fructose. In this work, we have deleted the TPS2 gene encoding tre -6-P phosphatase in a strain which displays very low levels of Ggs1/Tp s1, as a result of the presence of the byp1-3 allele of GGS1/TPS1. The byp1-3 tps2 Delta double mutant showed elevated tre-6-P levels along with improved growth and ethanol production, although the estimated co ncentrations of glycolytic metabolites indicated excessive sugar influ x. In the wild-type strain, the addition of glucose caused a rapid tra nsient increase of tre-6-P. In tps2 Delta mutant cells, which showed a high tre-6-P level before glucose addition, sugar influx into glycoly sis appeared to be diminished. Furthermore, we have confirmed that tre -6-P inhibits the hexokinases in vitro. These data are consistent with restriction of sugar influx into glycolysis through inhibition of the hexokinases by tre-6-P during the switch to fermentative metabolism. During logarithmic growth on glucose the tre-6-P level in wildtype cel ls was lower than that of the byp1-3 tps2 Delta mutant. However, the l atter strain arrested growth and ethanol production on glucose after a bout four generations. Hence, other mechanisms, which also depend on G gs1/Tps1, appear to control sugar influx during growth on glucose. In addition, we provide evidence that the requirement for Ggs1/Tps1 for s porulation may be unrelated to its involvement in trehalose metabolism or in the system controlling glycolysis.