Effect of altered sterol composition on growth characteristics of Saccharomyces cerevisiae.

The function of sterols in mitochondrial structures of yeast was examined. Sterol mutant strains were employed to examine the effects of altered sterolic content on optimal and permissive growth temperatures in respiring and fermenting cultures. Although fermentative growth was unaffected by sterol composition, a definite decrease in both the optimal and the permissive growth temperatures of respiring cultures was observed when ergosterol was replaced by Delta(8(9), 22)-ergostadiene-3beta-ol. In vitro studies showed a similar decrease in membrane phase transition temperatures of the mitochondrial enzyme S-adenosylmethionine: Delta(24)-sterol methyltransferase in the mutant strains. Increased sterol and methyltransferase levels were detected in strains incapable of synthesizing ergosterol. A possible control function governing sterol synthesis is proposed for ergosterol.