A MUTATION IN A PURPORTED REGULATORY GENE AFFECTS CONTROL OF STEROL UPTAKE IN SACCHAROMYCES-CEREVISIAE

Aerobically growing wild-type strains of Saccharomyces cerevisiae are unable to take exogenously supplied sterols from media. This aerobic s terol exclusion is vitiated under anaerobic conditions, in heme-defici ent strains, and under some conditions of impaired sterol synthesis. M utants which can take up sterols aerobically in heme-competent cells h ave been selected. One of these mutations, designated upc2-1, gives a pleiotropic phenotype in characteristics as diverse as aerobic accumul ation of sterols, total lipid storage, sensitivity to metabolic inhibi tors, response to altered sterol structures, and cation requirements. During experiments designed to ascertain the effects of various cation s on yeast with sterol alterations, it was observed that upc2-1 was hy persensitive to Ca2+. Using resistance to Ca2+ as a screening vehicle, we cloned UPC2 and showed that it is YDR213W, an open reading frame o n chromosome IV. This belongs to a fungal regulatory family containing the Zn(II)2Cys6 binuclear cluster DNA binding domain. The single guan ine-to-adenine transition in upc2-1 gives a predicted amino acid chang e from glycine to aspartic acid. The regulatory defect explains the se midominance and pleiotropic effects of upc2-1.