The cytochrome b5 dependent C-5(6) sterol desaturase DES5A from the endoplasmic reticulum of Tetrahymena thermophila complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae

► Ciliate DES5A gene restores ergosterol biosynthesis in erg3 Saccharomyces cerevisiae strain. ► DES5A gene reverses the hypersensitivity to cycloheximide in erg3 strain. ► Des5Ap is localized in endoplasmic reticulum of Tetrahymena thermophila and S. cerevisiae.