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Eukaryotic Cell, July 2006, p. 1018-1025, Vol. 5, No. 7
1535-9778/06/$08.00+0     doi:10.1128/EC.00002-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Yeh1 Constitutes the Major Steryl Ester Hydrolase under Heme-Deficient Conditions in Saccharomyces cerevisiae

René Köffel and Roger Schneiter*

Department of Medicine, Division of Biochemistry, University of Fribourg, 1700 Fribourg, Switzerland

Received 2 January 2006/ Accepted 4 May 2006

Steryl esters are stored in intracellular lipid droplets from which they are mobilized upon demand and hydrolyzed to yield free sterols and fatty acids. The mechanisms that control steryl ester mobilization are not well understood. We have previously identified a family of three lipases of Saccharomyces cerevisiae that are required for efficient steryl ester hydrolysis, Yeh1, Yeh2, and Tgl1 (R. Köffel, R. Tiwari, L. Falquet, and R. Schneiter, Mol. Cell. Biol. 25:1655-1668, 2005). Both Yeh1 and Tgl1 localize to lipid droplets, whereas Yeh2 is localized to the plasma membrane. To characterize the precise function of these three partially redundant lipases, we examined steryl ester mobilization under heme-deficient conditions. S. cerevisiae is a facultative anaerobic organism that becomes auxotrophic for sterols and unsaturated fatty acids in the absence of molecular oxygen. Anaerobic conditions can be mimicked in cells that are deficient for heme synthesis. We here report that Yeh1 is the sole active steryl ester hydrolase under such heme-deficient conditions, indicating that Yeh1 is activated whereas Yeh2 and Tgl1 are inactivated by the lack of heme. The heme-dependent activation of Yeh1 is mediated at least in part by an increase in steady-state levels of Yeh1 at the expense of Yeh2 and Tgl1 in exponentially growing cells. This increase in steady-state levels of Yeh1 requires Rox3, a component of the mediator complex that regulates transcription by RNA polymerase II. These data thus provide the first link between fat degradation and the transcriptional control of lipase activity in yeast.

* Corresponding author. Mailing address: University of Fribourg, Department of Medicine, Division of Biochemistry, Chemin du Musée 5, CH-1700 Fribourg, Switzerland. Phone: 41 26 300 8654. Fax: 41 26 300 9735. E-mail: roger.schneiter{at}unifr.ch.

Eukaryotic Cell, July 2006, p. 1018-1025, Vol. 5, No. 7
1535-9778/06/$08.00+0     doi:10.1128/EC.00002-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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