Tetracycline-regulatable system to tightly control gene expression in the pathogenic fungus Candida albicans

Conventional tools for elucidating gene function are relatively scarce in C andida albicans, the most prevalent human fungal pathogen. To this end, we developed a convenient system to control gene expression in C. albicans by the tetracycline-regulatable (TR) promoters. When the sea pansy Renilla ren iformis luciferase gene (RLUC1) was placed under the control of this system , doxycycline (DOX) inhibited the luciferase activity almost completely. In the absence of DOX, the RLUC1 gene was induced to express luciferase at a level 400- to 1,000-fold higher than that in the presence of DOX. The same results were obtained in hypha-forming cells. The replacement of N-myristoy ltransferase or translation elongation factor 3 promoters with TR promoters conferred a DOX-dependent growth defect in culture media. Furthermore, all the mice infected with these mutants, which are still virulent, survived f ollowing DOX administration. Consistently, we observed that the number of t hese mutant cells recovered from the mouse kidneys was significantly reduce d following DOX administration. Thus, this system is useful for investigati ng gene functions, since this system is able to function in both in vitro a nd in vivo settings.