Functional isolation of the Candida albicans FCR3 gene encoding a bZip transcription factor homologous to Saccharomyces cerevisiae Yap3p

We have isolated a C albicans gene, named FCR3 (for fluconazole resistance 3), based upon its ability to suppress the FCZ hypersusceptibility of a Sac charomyces cerevisiae mutant strain (JY312) lacking the transcription facto rs Pdr1p and Pdr3p. The FCR3 ORF (1200 bp) encodes a 399 amino acid protein containing a basic leucine zipper (bZip) domain. Fcr3p displays the highes t level of sequence homology with the S. cerevisiae Yap3p protein (34%, ide ntity, 45% similarity). We had previously shown that deletion of the PDR5 g ene encoding a multidrug transporter completely abolished the ability of FC R3 to suppress the FCZ hypersusceptibility of JY312, suggesting that FCR3 c onfers FCZ resistance by activating PDR5 expression. We show here that the fl-galactosidase activity of a PDR5 promoter-lacZ construct in, JY312 is in creased two-fold upon FCR3 overexpression, demonstrating that FCR3 regulate s PDR5 at the transcriptional level. We also show that FCR3 overexpression riot only suppresses the hypersusceptibility of JY312 to 4-nitroquinoline-N -oxide (4-NQO) but also confers higher levels of resistance to this compoun d as compared to the wild-type KY320 strain. Since PDR5 is not involved in 4-NQO resistance, this result indicates that FCR3 can also activate the tra nscription of other genes that can confer 4-NQO resistance. Finally, Northe rn blot analysis indicates that FCR3 encodes a single 2.4 kb RNA transcript in C. albicans, suggesting that the FCR3 mRNA contains long 5' and/or 3' u ntranslated regions. The nucleotide sequence of the FCR3 gene has been depo sited at GenBank under Accession No. AF342983. Copyright (C) 2001 John Wile y & Sons, Ltd.