The Effects of Varied Energy Source and Detergent on the Growth of Sterol Mutants of Saccharomyces cerevisiae

Abstract

The effects of altered membrane sterol composition on the growth characteristics of sterol mutants of Saccharomyces cerevisiae were determined using various energy sources and the detergent Tergitol. These mutants do not synthesize the end-product sterol, ergosterol, but do not require exogenous sterol for growth. The sterol biosynthetic intermediates that are incorporated into the mutant membranes are related to alterations in growth characteristics. The C-24 transmethylation step (erg6) was shown to be critical to membrane integrity. Cells with this lesion were protected by the presence of Tergitol or glycerol in the medium. A double mutant (erg6/2), containing the Δ8 → Δ7 isomerization lesion (erg2) and the C-24 transmethylation lesion (erg6), was highly sensitive to ethanol and Tergitol. These results corroborate permeability and membrane fluidity studies indicating that C27 sterols are much less efficient than C28 sterols in maintaining normal membrane structure and function.