Differences in the cytochrome P-450 enzymes of sterol C-14 demethylase mutants of Saccharomyces cerevisiae.

A number of nystatin-resistant strains of S. cerevisiae have been isolated which are defective in lanosterol C-14 demethylation, a reaction normally catalysed by cytochrome P-450. In this paper two of these strains have been compared and found to have differences in their reduced-CO difference spectra indicating different distortions in the enzyme molecule. Nystatin resistance in the C-14 demethylation deficient SG1 in shown to be determined by a single gene, and a sterol 5,6-desaturase defect does not appear to be required for viability of SG1, was reported for the C-14 demethylase deficient isolate JR4 by Taylor et al. (1983). There are at least two discernable mutant phenotypes for the yeast cytochrome P-450 structural gene which give a C-14 demethylase defect.