BIOCHEMICAL AND PHYSIOLOGICAL-EFFECTS OF STEROL ALTERATIONS IN YEAST - A REVIEW

Considerable progress has been made in the selection and characterizat ion of mutants that are defective in the synthesis of ergosterol in th e yeast, Saccharomyces cerevisiae. Mutations in nearly every step of t he yeast sterol biosynthetic pathway have been induced and selected. T hese mutants have been used to elucidate the sequential order of steps in sterol synthesis, to study the mode of action of antifungal agents and to determine the method of resistance of some pathogenic fungi, a nd to answer questions on the role of sterols in general cell biology. Physiological examination of ergosterol null mutants, lacking all bio chemical activity attributed to the particular gene, supports a role f or ergosterol in a number of critical functions in the organism. Among the physiological functions attributed to ergosterol are sparking and bulking requirements, involvement in amino acid and pyrimidine transp ort, resistance to antifungal agents and certain cations, and a requir ement for respiratory activity. Those genetic null alleles discussed i n this review are erg24, lacking the ability to reduce the Delta(14) d ouble bond; erg6, unable to methylate C-24; and erg3, defective in the C-5 desaturase. The different biochemical activities that are disrupt ed in the ergosterol mutants support a role for ergosterol in a number of critical functions in yeast.