Abstract
Controllable regulatory elements, like inducible, titratable promoters, are highly desired in synthetic biology toolboxes. A set of previously developed erythritol-inducible promoters along with an engineered Yarrowia lipolytica host strain were shown to be a very potent expression platform. In this study, we push the previously encountered limits of the synthetic promoters' titratability (by the number of upstream motifs) by using a compatible transcription factor, Euf1, as the promoter titrator. Overexpression of spliced EUF1 turned out to be very efficient in promoting expression from the compatible promoter, however, the erythritol-inducible character of the promoter was then lost. Analysis of the EUF1's splicing pattern suggests that the intron removal is promoted in the presence of erythritol, but is not dependent on it. The 3D structures of spliced versus unspliced Euf1 were modeled, and ligand-binding strength was calculated and compared. Furthermore, the EUF1-dependent expression profile under different chemical stimulants was investigated. Depletion of carbon source was identified as the significant factor upregulating the expression from the Euf1-dependent promoter (2-10-fold). Considering these findings and transcriptomics data, a new mechanism of the Euf1-regulated promoter action is proposed, involving a 'catabolite repression' transcription factor-Adr1, both acting on the same ERY-inducible promoter.