Genetic Analysis of Azole Resistance by Transposon Mutagenesis in Saccharomyces cerevisiae

The increasing resistance of Candida species to fluconazole is cause for concern. To determine the molecular mechanisms involved in resistance to fluconazole, I used a scheme of transposon mutagenesis in Saccharomyces cerevisiae, a genetically tractable yeast that is closely related to Candida albicans. This technique, which permits the generation and analysis of multiple random Tn3::LEU2::lacZ fusions, can be used as a disruption mutagen (N. B. Burns et al., Genes Dev. 8:1087–1105, 1994). By using the Tn3::LEU2::lacZ library as a disruption mutagen, I found recessive mutations in genes that were previously found to be involved in azole resistance, e.g., PDR5 and CPR1, and in genes previously found to be involved in azole sensitivity, e.g., ERG3. This approach also enabled me to identify recessive mutations in three genes not previously known to be involved in azole sensitivity. Two of the genes, ADA3 and SPT7, are general transcriptional regulators; the third, YMR034c, is a putative sterol transporter. Finally, by screening the Tn3::LEU2::lacZ library for lacZ fusions induced by a low concentration of fluconazole, I identified genes known to be induced by azoles as well as a variety of other genes not previously known to be induced by the drug. In conclusion, transposon mutagenesis is a promising screening tool for use in identifying novel drug targets and in uncovering the mechanisms involved in the response of S. cerevisiae to antifungal drugs.