ISOLATION AND CHARACTERIZATION OF A GENE AFFECTING FATTY-ACID ELONGATION IN SACCHAROMYCES-CEREVISIAE

Fatty acid elongation defective mutants were isolated from Saccharomyc es cerevisiae by mutagenizing strains that were defective in fatty aci d synthase (FAS) activity, Cells of the fatty acid synthase-defective strains can grow when supplemented with tetradecanoic acid (14:0) due to the presence of membrane bound elongation systems that can extend t he 14 carbon fatty acid to longer chain species, After mutagenesis and rescue on medium containing a mixture of 14:0, 16:0 and 18:0, cells w ere screened for their inability to grow on medium containing only 14: 0, From 150,000 colonies, four stable isolates were identified, all of which appear to represent the same complementation group, Gas chromat ography of lipid extracts from mutant elo1-1 (designated as elongation defective) cells grown with long or medium chain fatty acids indicate s that it fails to efficiently elongate (12, 13, or 14) carbon fatty a cids, A gene disrupted fas2 Delta::LEU2;elo1 Delta::HIS3 mutant incorp orates 14-18-carbon fatty acids into membrane lipids, indicating that fatty acid transport is not affected by the mutation, Molecular clonin g and sequence analysis of the ELO1 gene suggests that the encoded pro tein is a membrane bound polypeptide that contains at least five poten tial membrane spanning regions and a presumptive NADPH binding site, A nalysis of the ELO1 mRNA levels indicates that the gene is expressed i n cells grown on fatty acid deficient medium, It is rapidly induced in wild type cells that are supplemented with 14:0 and is repressed when cells are supplied with 16- and 18-carbon fatty acids.