AP1-MEDIATED MULTIDRUG-RESISTANCE IN SACCHAROMYCES-CEREVISIAE REQUIRES FLR1 ENCODING A TRANSPORTER OF THE MAJOR FACILITATOR SUPERFAMILY

We have isolated a Candida albicans gene that confers resistance to th e azole derivative fluconazole (FCZ) when overexpressed in Saccharomyc es cerevisiae. This gene encodes a protein highly homologous to S. cer evisiae yAP-1, a bZip transcription factor known to mediate cellular r esistance to toxicants such as cycloheximide (CYH), 4-nitroquinoline N -oxide (4-NQO), cadmium, and hydrogen peroxide. The gene was named CAP 1, for C. albicans AP-1. Cap1 and yAP-1 are functional homologues, sin ce CAP1 expression in a yap1 mutant strain partially restores the abil ity of the cells to grow on toxic concentrations of cadmium or hydroge n peroxide. We have found that the expression of YBR008c, an open read ing frame identified in the yeast genome sequencing project and predic ted to code for a multidrug trans porter of the major facilitator supe rfamily, is dramatically induced in S. cervisiae cells overexpressing CAP1. Overexpression of either CAP1 or YAP1 in a wild type strain resu lts in resistance to FCZ, CYH, and 4-NQO, whereas such resistance is c ompletely abrogated (FCZ and CYH) or strongly reduced (4-NQO) in a ybr 008c deletion mutant, demonstrating that YBR008c is involved in YAP1- and CAP1-mediated multidrug resistance. YBR008c has been renamed FLR1, for fluconazole resistance 1. The expression of an FLR1-lacZ reporter construct is strongly induced by the overexpression of either CAP1 or YAP1, indicating that the FLR1 gene is transcriptionally regulated by the Cap1 and yAP-1 proteins. Taken collectively, our results demonstr ate that FLR1 represents a new YAP1-controlled multidrug resistance mo lecular determinant in S. cerevisiae, A similar detoxification pathway is also likely to operate in C. albicans.