Yarrowia lipolytica, like other lower fungi, has a fatty acid synthetase complex (FAS) with an a& molecular structure. Both subunits are multifunctional proteins each with a molecular weight of more then 200000 daltons. A collection of FAS-deficient?) Y. Zipolyticu 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 /l and, therefore, are encoded by the gene locus F A S l . /l-Ketoacyl reductase, /l-ketoacyl synthase and acyl carrier protein functions are part of the FAS2-encoded subunit a. Thus, the functional organization of F A S l and F A S B is identical in both yeasts, Smharomycea cerevisiae and Yarrowiu lipolytica. Nevertheless, the two yeasts differ significantly with respect to the intragenic complementation characteristics of fael and f a 2 mutants. This finding is discussed in terms of a specific inter-or intramolecular reaction mechanism within the oligomeric FAS complex. The pentafunctional Y. liplytica F A S l gene was isolated from a lgtll expression library using polyclonal antisera against the purified FAS complex. At present, sequencing of F A S l , 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 /l of the two yeasts, Y. lipolytica and S. cerevisiue.
Fungal fatty acid synthetases (FAS) are multienzyme complexes with eight different catalytic centres distributed on two exceptionally large (> 200000 daltons mol.wt.) subunits, u and /? (LYNEN 1980). In saccharomyces cerevisiae, subunit u is trifunctional harboring the /?-ketoacyl reductase, the /?-ketoacyl synthase and the acyl carrier protein, while the pentafunctional subunit/? contains the acetyl-, malonyl-and palmityl transferases, the dehydratase and the enoyl reductase active sites. The intact PAS complex is an a&, oligomer of these tri-and pentafunctional subunits, respectively. From Saccharomyces cerevisiae, the fatty acid synthetase genes PAS1 and PAS2 encoding, respectively, /? and u have recently been isolated and sequenced ( SCHWEIZER