CLONING AND CHARACTERIZATION OF THE SACCHAROMYCES-CEREVISIAE C-22 STEROL DESATURASE GENE, ENCODING A 2ND CYTOCHROME-P-450 INVOLVED IN ERGOSTEROL BIOSYNTHESIS

The ERGS gene from Saccharomyces cerevisiae was cloned by complementat ion of an erg5-1 mutation using a negative selection protocol involvin g screening for nystatin-sensitive transformants. ERG5 is the putative gene encoding the C-22 sterol desaturase required in ergosterol biosy nthesis. The functional gene was localized to a 2.15-kb SacI-EcoRI DNA fragment containing an open reading frame of 538 amino acids (aa), ER GS contains a 10-aa motif consistent with its role as a cytochrome P-4 50 (CyP450) enzyme and is similar to a number of mammalian CyP450 enzy mes. Gene disruption demonstrates that ERG5 is not essential for cell viability.