PHYSIOLOGICAL IMPLICATIONS OF STEROL BIOSYNTHESIS IN YEAST

Fungi are among the most primitive organisms that synthesize sterols. The fungal sterol, ergosterol, is similar to animal sterol, cholestero l, but with significant structural differences. The genetics and bioch emistry for most of the steps in sterol biosynthesis have been studied in the yeast, Saccharomyces cerevisiae. Yet, little is known of the p recise physiological roles that sterols play in the cell. Work with st rains that are auxotrophic for ergosterol has led to the prediction of at least four growth-dependent functions for sterols. Most of the ant ifungal compounds in medical and agricultural use affect some aspect o f sterol synthesis or function. Extensive studies on the modes of acti on of those substances and research on the effects of altering sterol metabolism by sterol mutants are providing new insights into sterol fu nctions in the cells. In addition, questioning why fungi require ergos terol rather than the simpler cholesterol provides heuristic impetus f or further experimentation.