Genetic control of Yarrowia lipolytica fatty acid synthetase biosynthesis and function

Yarrowia lipolytica, like other lower fungi, has a fatty acid synthetase complex (FAS) with an alpha 6 beta 6 molecular structure. Both subunits are multifunctional proteins each with a molecular weight of more then 200,000 daltons. A collection of FAS-deficient) Y. lipolytica mutants was isolated and characterized by both genetic complementation and enzyme activity measurements. It was found that the three acyl transferases (acetyl-, malonyl- and palmityl-transacylation) together with the enoyl reductase domain are located on subunit beta and, therefore, are encoded by the gene locus FAS1. beta-Ketoacyl reductase, beta-ketoacyl synthase and acyl carrier protein functions are part of the FAS2-encoded subunit alpha. Thus, the functional organization of FAS1 and FAS2 is identical in both yeasts, Saccharomyces cerevisiae and Yarrowia lipolytica. Nevertheless, the two yeasts differ significantly with respect to the intragenic complementation characteristics of fas1 and fas2 mutants. This finding is discussed in terms of a specific inter- or intramolecular reaction mechanism within the oligomeric FAS complex. The pentafunctional Y. lipolytica FAS1 gene was isolated from a lambda gt11 expression library using polyclonal antisera against the purified FAS complex. At present, sequencing of FAS1, which is more than 5 kilobases long, is almost completed. Available data indicate approx. 60 percent sequence homology together with an identical order of catalytic domains within subunit beta of the two yeasts, Y. lipolytica and S. cerevisiae.