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Molecular and Cellular Biology, August 2005, p. 7375-7385, Vol. 25, No. 16
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.16.7375-7385.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Dual Activators of the Sterol Biosynthetic Pathway of Saccharomyces cerevisiae: Similar Activation/Regulatory Domains but Different Response Mechanisms

Brandon S. J. Davies, Helen S. Wang, and Jasper Rine*

Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720

Received 18 March 2005/ Returned for modification 15 April 2005/ Accepted 31 May 2005

Genes encoding biosynthetic enzymes that make ergosterol, the major fungal membrane sterol, are regulated, in part, at the transcriptional level. Two transcription factors, Upc2p and Ecm22p, bind to the promoters of most ergosterol biosynthetic (ERG) genes, including ERG2 and ERG3, and activate these genes upon sterol depletion. We have identified the transcriptional activation domains of Upc2p and Ecm22p and found that UPC2-1, a mutation that allows cells to take up sterols aerobically, increased the potency of the activation domain. The equivalent mutation in ECM22 also greatly enhanced transcriptional activation. The C-terminal regions of Upc2p and Ecm22p, which contained activation domains, also conferred regulation in response to sterol levels. Hence, the activation and regulatory domains of these proteins overlapped. However, the two proteins differed markedly in how they respond to an increased need for sterols. Upon inducing conditions, Upc2p levels increased, and chromatin immunoprecipitation experiments revealed more Upc2p at promoters even when the activation/regulatory domains were tethered to a different DNA-binding domain. However, induction resulted in decreased Ecm22p levels and a corresponding decrease in the amount of Ecm22p bound to promoters. Thus, these two activators differ in their contributions to the regulation of their targets.

* Corresponding author. Mailing address: Department of Molecular and Cell Biology, University of California at Berkeley, 522 Barker Hall, Berkeley, CA 94720-3202. Phone: (510) 642-7047. Fax: (510) 642-6420. E-mail: jrine{at}berkeley.edu.

Molecular and Cellular Biology, August 2005, p. 7375-7385, Vol. 25, No. 16
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.16.7375-7385.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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