Hexokinase regulates kinetics of glucose transport and expression of genesencoding hexose transporters in Saccharomyces cerevisiae

Glucose transport kinetics and mRNA levels of different glucose transporter s were determined in Saccharomyces cerevisiae strains expressing different sugar kinases, During exponential growth on glucose, a hxk2 null strain exh ibited high-affinity hexose transport associated with an elevated transcrip tion of the genes HXT2 and HXT7, encoding high-affinity transporters, and a diminished expression of the HXT1 and HXT3 genes, encoding low-affinity tr ansporters. Deletion of HXT7 revealed that the high-affinity component is m ostly due to HXT7; however, a previously unidentified very-high-affinity co mponent (K-m = 0.19 mM) appeared to be due to other factors. Expression of genes encoding hexokinases from Schizosaccharomyces pombe or Yarrowia lipol ytica in a hrk1 hxk2 glk1 strain prevented derepression of the high-affinit y transport system at high concentrations of glucose.