Spot plate analysis of erg27 mutant yeast strains transformed with p426GPD containing the human, mouse, or yeast 3-ketoreductase. Strains were grown on SC-Ura media containing glucose supplemented with either lanosterol, ergosta-7,22-diene-3-one (precursor to Erg27p), ergosterol or Tween 80 (control). Serial dilutions of 105-102 cells were spotted onto indicated plates. Pictures were taken after 3 days growth. Strains expressing mammalian steroid-3-ketoreductase complement very poorly the erg27 yeast strain in the absence of exogenous sterol; however they complement well in the presence of ergosta-7,22-diene-3-one.