Sterol metabolism and ERG2 gene regulation in the yeast Saccharomyces cerevisiae

Certain exogenously-supplied sterols, like ergost-8-enol. are efficiently c onverted into ergosterol in yeast, We have taken advantage of this property to study the regulation of the Delta 8-Delta 7-sterol isomerase-encoding E RG2 gene in an ergosterol auxotrophic mutant devoid of squalene-synthase ac tivity. Ergosterol starvation leads to an 8-16-fold increase in ERG2 gene e xpression, Such an increase was also observed in wild-type cells either gro wn anaerobically or treated with SR31747A a sterol isomerase inhibitor. Exo genously-supplied zymosterol is entirely transformed into ergosterol, which represses ERG2 transcription. By contrast, exogenously-supplied ergosterol has little or no effect on ERG2 transcription. (C) 2000 Federation of Euro pean Biochemical Societies.