The Sef1 transcription factor interacts with promoters of riboflavin structural genes in Candida famata

Riboflavin (RF, vitamin B2) serves as a precursor for the flavin coenzymes FAD and FMN, which are involved in numerous redox reactions in cells. RF is produced on an industrial scale. The yeast Candida famata overproduces RF under iron-starvation conditions, and mutants have been isolated that accumulate large amounts of RF. Overexpression of Sef1, the transcription factor of the zinc cluster family, increases RF production in C. famata; however, the specific mechanism remains unknown. Here, we report that SEF1 expression is upregulated under iron deficiency. We developed a yeast one-hybrid system based on the yeast Saccharomyces cerevisiae to study the role of Sef1 in regulation of RF biosynthesis. We found that Sef1 activates the promoters of the RIB1, RIB3, RIB5, RIB6, and RIB7 genes. Additionally, SEF1 was shown to undergo autoregulation. For the RIB1 promoter, a Sef1-binding sequence has been identified. The ability of Sef1 to activate RIB genes expression was further validated in the native C. famata system.