Isolation of temperature-sensitive Saccharomyces cerevisiae with a mutation in erg25 for C-4 sterol methyl oxidase

C-4 sterol methyl oxidase encoded by the ERG25 gene is a key enzyme in the ergosterol biosynthetic pathway in fungi. ERG25p contains three histidine clusters common to nonheme iron binding enzymes and endoplasmic reticulum retrieval signal. In order to characterize ERG25p, we generated a series of temperature-sensitive(ts) erg25 mutants by random mutagenesis. One of the resulting mutants, the mERG25 strain, accumulated 4,4-dimethlzymosterol at the nonpermissive temperature. Sequence analysis of the mERG25 mutant indicated three amino acid substitutions in ERG25p, namely N48D, V133A, and F135S. These results indicate that the ERG25 gene product is a new antifungal target.