PEROXISOMAL DELTA-3-CIS-DELTA-2-TRANS-ENOYL-COA ISOMERASE ENCODED BY ECI1 IS REQUIRED FOR GROWTH OF THE YEAST SACCHAROMYCES-CEREVISIAE ON UNSATURATED FATTY-ACIDS

We have identified the Saccharomyces cerevisiae gene ECI1 encoding Del ta(3)-cis-L-Delta(2)-trans-enoyl-CoA isomerase that acts as an auxilia ry enzyme in the beta-oxidation of (poly)unsaturated fatty acids. A mu tant devoid of Eci1p was unable to grow on media containing unsaturate d fatty acids such as oleic acid but was proficient for growth when a saturated fatty acid such as palmitic acid was the sole carbon source. Levels of ECI1 transcript were elevated in cells grown on oleic acid medium due to the presence in the ECI1 promoter of an oleate response element that bound the transcription factors Pip2p and Oaf1p. Eci1p wa s heterologously expressed in Escherichia coli and purified to homogen eity. It was found to be a hexameric protein with a subunit of molecul ar mass 32,000 Da that converted 3-hexenoyl-CoA to trans-2-hexenoyl-Co A Eci1p is the only known member of the hydratase/isomerase protein fa mily with isomerase and/or 2-enoyl-CoA hydratase 1 activities that doe s not contain a conserved glutamate at its active site. Using a green fluorescent protein fusion, Eci1p was shown to be located in peroxisom es of wild-type yeast cells. Rat peroxisomal multifunctional enzyme ty pe I containing Delta(3)-cis-Delta(2)-trans-enoyl-CoA isomerase activi ty was expressed in ECI1-deleted yeast cells, and this restored growth on oleic acid.