Eukaryotic Cell
The azole antifungal drugs are used to treat infections caused by Candida albicans and other fungi. These drugs interfere with the biosynthesis of ergosterol, the major sterol in fungal cells, by inhibiting an ergosterol biosynthetic enzyme, lanosterol 14 alpha-demethylase, encoded by the ERG11 gene. In vitro, these drugs as well as other ergosterol biosynthesis inhibitors increase ERG11 mRNA expression by activation of the ERG11 promoter. The signal for this activation most likely is the depletion of ergosterol, the end product of the pathway. To identify cis-acting regulatory elements that mediate this activation, ERG11 promoter fragments have been fused to the luciferase reporter gene from Renilla reniformis. Promoter deletions and linker scan mutations localized the region important for azole induction to a segment from bp -224 to -251 upstream of the start codon, specifically two 7-bp sequences separated by 13 bp. These sequences form an imperfect inverted repeat. The region is recognized by the transcription factor Upc2p and functions as an enhancer of transcription, as it can be placed upstream of a heterologous promoter in either direction, resulting in the azole induction of that promoter. The promoter constructs are not azole inducible in the upc2/upc2 homozygous deletion, demonstrating that Upc2p controls the azole induction of ERG11. These results identify an azole-responsive enhancer element (ARE) in the ERG11 promoter that is controlled by the Upc2p transcription factor. No other ARE is present in the promoter. Thus, this ARE and Upc2p are necessary and sufficient for azole induction of ERG11.