Expression of one-hybrid fusions with Staphylococcus aureus lexA in Candida albicans confirms that Nrg1 is a transcriptional repressor and that Gcn4 is a transcriptional activator

In the pathogenic fungus, Candida albicans, Nrg1 down-regulates the expression of morphogenetic genes and is presumed to act as a transcriptional repressor. In contrast, Gcn4 up-regulates amino acid biosynthetic genes and is presumed to be a transcriptional activator. However, these presumptions remain to be tested directly. A classic approach has been to use a one-hybrid assay that exploits the Escherichia coli lexA protein fusions. However in C. albicans, the alternate decoding of CUG as serine prevents the expression of heterologous genes such as lexA, which contain numerous CUG codons. Therefore, we have developed a one-hybrid system, based on the Staphylococcus aureus lexA gene, as a tool for one-hybrid analyses of transcription factors in C. albicans. Using this one-hybrid system we have confirmed directly the positive and negative transcriptional activities of Nrg1 and Gcn4 in C. albicans.