Fine-tuning the expression of target genes using a DDI2 promoter gene switch in budding yeast

Tuned gene expression is crucial to the proper growth and response to the environmental changes of an organism. To enable tunable gene expression as designed is desirable in both scientific research and industrial application. Here, we introduce a novel promoter switching method based on the DDI2 promoter (P(DDI2)) that can fine tune the expression of target genes. We constructed a recyclable cassette (P(DDI2)-URA3-P(DDI2)) and integrated it upstream of yeast target genes to replace the native promoters by DDI2 promoter without introducing any junk sequence. We found that the presence or absence of cyanamide as an inducer could turn on or off the expression of target genes. In addition, we showed that P(DDI2) could act as a gene switch to linearly regulate the expression levels of target genes in vivo. We switched the original promoters of RAD18, TUP1, and CDC6 with P(DDI2) as a proof-of-concept.