The pathogenic yeast Candida albicans can develop resistance to the widely used 
antifungal agent fluconazole, which inhibits ergosterol biosynthesis, by the 
overexpression of genes encoding multidrug efflux pumps or ergosterol 
biosynthesis enzymes. Zinc cluster transcription factors play a central role in 
the transcriptional regulation of drug resistance. Mrr1 regulates the expression 
of the major facilitator MDR1, Tac1 controls the expression of the ABC 
transporters CDR1 and CDR2, and Upc2 regulates ergosterol biosynthesis (ERG) 
genes. Gain-of-function mutations in these transcription factors result in 
constitutive overexpression of their target genes and are responsible for 
fluconazole resistance in many clinical C. albicans isolates. The transcription 
factor Ndt80 contributes to the drug-induced upregulation of CDR1 and ERG genes 
and also binds to the MDR1 and CDR2 promoters, suggesting that it is an 
important component of all major transcriptional mechanisms of fluconazole 
resistance. However, we found that Ndt80 is not required for the induction of 
MDR1 and CDR2 expression by inducing chemicals. CDR2 was even partially 
derepressed in ndt80Δ mutants, indicating that Ndt80 is a repressor of CDR2 
expression. Hyperactive forms of Mrr1, Tac1, and Upc2 promoted overexpression of 
MDR1, CDR1/CDR2, and ERG11, respectively, with the same efficiency in the 
presence and absence of Ndt80. Mrr1- and Tac1-mediated fluconazole resistance 
was even slightly enhanced in ndt80Δ mutants compared to wild-type cells. These 
results demonstrate that Ndt80 is dispensable for the constitutive 
overexpression of Mrr1, Tac1, and Upc2 target genes and the increased 
fluconazole resistance of strains that have acquired activating mutations in 
these transcription factors.